Probiotics in Medicine: A Long Debate

Abstract

During the last years probiotics gained the attention of clinicians for their use in the prevention and treatment of multiple diseases. Probiotics main mechanisms of action include enhanced mucosal barrier function, direct antagonism with pathogens, inhibition of bacterial adherence and invasion capacity in the intestinal epithelium, boosting of the immune system and regulation of the central nervous system. It is accepted that there is a mutual communication between the gut microbiota and the liver, the so-called “microbiota-gut-liver axis” as well as a reciprocal communication between the intestinal microbiota and the central nervous system through the “microbiota-gut-brain axis.” Moreover, recently the “gut-lung axis” in bacterial and viral infections is considerably discussed for bacterial and viral infections, as the intestinal microbiota amplifies the alveolar macrophage activity having a protective role in the host defense against pneumonia. The importance of the normal human intestinal microbiota is recognized in the preservation of health. Disease states such as, infections, autoimmune conditions, allergy and other may occur when the intestinal balance is disturbed. Probiotics seem to be a promising approach to prevent and even reduce the symptoms of such clinical states as an adjuvant therapy by preserving the balance of the normal intestinal microbiota and improving the immune system. The present review states globally all different disorders in which probiotics can be given. To date, Stronger data in favor of their clinical use are provided in the prevention of gastrointestinal disorders, antibiotic-associated diarrhea, allergy and respiratory infections. We hereby discuss the role of probiotics in the reduction of the respiratory infection symptoms and we focus on the possibility to use them as an adjuvant to the therapeutic approach of the pandemic COVID-19. Nevertheless, it is accepted by the scientific community that more clinical studies should be undertaken in large samples of diseased populations so that the assessment of their therapeutic potential provide us with strong evidence for their efficacy and safety in clinical use.

Full text

REVIEW
published: 25 September 2020
doi: 10.3389/fimmu.2020.02192
Frontiers in Immunology | www.frontiersin.org 1September 2020 | Volume 11 | Article 2192
Edited by:
Reinaldo B. Oria,
Federal University of Ceara, Brazil
Reviewed by:
Zhanju Liu,
Tongji University, China
Mariana Carmen Chifiriuc,
University of Bucharest, Romania
*Correspondence:
Elisavet Stavropoulou
elisabeth.stavropoulou@gmail.com
Specialty section:
This article was submitted to
Nutritional Immunology,
a section of the journal
Frontiers in Immunology
Received: 12 May 2020
Accepted: 11 August 2020
Published: 25 September 2020
Citation:
Stavropoulou E and Bezirtzoglou E
(2020) Probiotics in Medicine: A Long
Debate. Front. Immunol. 11:2192.
doi: 10.3389/fimmu.2020.02192
Probiotics in Medicine: A Long
Debate
Elisavet Stavropoulou 1,2
*and Eugenia Bezirtzoglou 3
1CHUV (Centre Hospitalier Universitaire Vaudois), Lausanne, Switzerland, 2Department of Infectious Diseases, Central
Institute, Valais Hospital, Sion, Switzerland, 3Laboratory of Hygiene and Environmental Protection, Department of Medicine,
Democritus University of Thrace, Alexandroupolis, Greece
During the last years probiotics gained the attention of clinicians for their use in the
prevention and treatment of multiple diseases. Probiotics main mechanisms of action
include enhanced mucosal barrier function, direct antagonism with pathogens, inhibition
of bacterial adherence and invasion capacity in the intestinal epithelium, boosting of
the immune system and regulation of the central nervous system. It is accepted that
there is a mutual communication between the gut microbiota and the liver, the so-
called “microbiota-gut-liver axis” as well as a reciprocal communication between the
intestinal microbiota and the central nervous system through the “microbiota-gut-brain
axis.” Moreover, recently the “gut-lung axis” in bacterial and viral infections is considerably
discussed for bacterial and viral infections, as the intestinal microbiota amplifies the
alveolar macrophage activity having a protective role in the host defense against
pneumonia. The importance of the normal human intestinal microbiota is recognized in
the preservation of health. Disease states such as, infections, autoimmune conditions,
allergy and other may occur when the intestinal balance is disturbed. Probiotics seem to
be a promising approach to prevent and even reduce the symptoms of such clinical states
as an adjuvant therapy by preserving the balance of the normal intestinal microbiota and
improving the immune system. The present review states globally all different disorders
in which probiotics can be given. To date, Stronger data in favor of their clinical use are
provided in the prevention of gastrointestinal disorders, antibiotic-associated diarrhea,
allergy and respiratory infections. We hereby discuss the role of probiotics in the reduction
of the respiratory infection symptoms and we focus on the possibility to use them as an
adjuvant to the therapeutic approach of the pandemic COVID-19. Nevertheless, it is
accepted by the scientific community that more clinical studies should be undertaken
in large samples of diseased populations so that the assessment of their therapeutic
potential provide us with strong evidence for their efficacy and safety in clinical use.
Keywords: probiotics, medicine, intestine, COVID-19, lung, allergy, Lactobacillus,Bifidobacterium
Probiotics are living non-pathogenic microorganisms, which when given in sufficient amounts (at
least 106viable CFU/g) should be beneficial to host by improving its microbial balance in gut and
participate in the metabolism (1).
Moreover, probiotics are known to have particular properties such as; resistance to acid pH,
bile tolerance, tolerance to pancreatic fluid, adhesion and invasion capacity in the intestinal
epithelial cells (2). The above properties permit their survival in the gastrointestinal tract and the
improvement of the intestinal balance (2).

Stavropoulou and Bezirtzoglou Probiotics in Medicine
During the past years, the use of probiotic microorganisms
has been applied to modulate the microbiome in a beneficial
way and thus fighting against infections threatening human and
animal health (3). Their use might sometimes be an alternative
to antibiotics permitting to reduce antimicrobial resistance due
to the overuse or misuse of antibiotics against infections (4,
5). Spreading of antibiotic resistance is a major public health
problem among human pathogens (4). The development of
antibiotic resistance through different mechanisms may result in
unsuccessful treatment of infectious diseases.
Nevertheless, neither the FDA, more the EFSA have approved
the use of probiotics for preventing or treating health issues,
despite their classification as safe food supplements (6,7).
Both authorities have punctuated the faulty characterization
and health claims, the scarcity of an efficient explanation
of their mechanism of action as well as the failing of
considerable studies in humans to really show a benefit of the
probiotics’ administration.
The Japanese Ministry of Health and Welfare seems to have a
different policy. FOSHU label (Food for Specified Health Use) is
given to a specific probiotic product allowing health claims (8).
Lactobacillus and Bifidobacterium genera are principally
reported as probiotics. These bacterial genera are isolated in
the human intestine in considerable populations. Lactobacillus
includes different species with the most semantic as probiotics;
L. acidophilus, L. rhamnosus, L. bulgaricus, L. reuteri, L. casei,
L. johnsonii, L. pantarum. These strains are acid-tolerant in
the stomach acidity and have a good adherence capacity to
the intestinal cells. Bifidobacterium belong to the phylum of
Actinobacteria as they have a characteristic ramified morphology.
The most common Bifidobacterium probiotic species are B.
animalis, B. bifidum, B. breve, B. infantis, B. lactis, B. longum.
Streptococcus thermophilus, Enterococcus faecalis,
Enterococcus faecium, Pediococcus, and several Bacilli, as
well as the yeasts Saccharomyces boulardii and Saccharomyces
cerevisiae also show some probiotic properties.
Probiotic microorganisms are part of our intestinal flora,
yet they can also be found in other ecological environments.
However, it must be clear that probiotic properties are strain-
related and even tissue-dependent. Thus, the probiotic effect
neither universal to all bacterial species nor to all human tissues.
Early intestinal colonization seems to provide protection
against certain diseases by strengthening our immune system
(1). Until now, it is not known which bacterial species are
necessary to induce an appropriate and effective “barrier effect”
against pathogens, but it seems that this “barrier effect” can
be strongly supported by providing beneficial food supplements
called probiotics (3). Specifically, through this type of diet
a beneficial microbiota dominated by Lactobacilli (phylum of
Firmicutes) and Bifidobacteria (phylum of Actinobacteria) is
registered (9).
International Scientific Association for Probiotics and
Prebiotics (2014) (8) declared that metabolic by-products,
bacterial molecular components and dead microorganisms
might have some beneficial effect; despite the real conviction
that a probiotic must have a high ability to survive under
intestinal conditions (acidic pH, enzymes, bile salts, etc.) and
that their activity and effectiveness are linked to viability (10).
Currently, the term “postbiotic” is developed for soluble bacterial
components with biological activities which are believed to be
safer than the use of whole bacteria (11).
Multiple studies on the probiotic strains’ characteristics
have been done, including biochemical profile, adherence
and invasion capacities to intestinal cells (12). Moreover,
pharmacokinetic studies (half - life time, intestinal permeability,
correlation of the obtained dose and persistence in stools) have
been reported (13) as well as studies on the tolerance of the
probiotic strain by the host and its input on the bacterial
microflora (14). All the above tests and studies have permitted
to characterize by the Food and Drug Administration (FDA)
(USA) a probiotic given strain under the acronym of “GRAS”
(Generally Recognized As Safe), meaning a food supplement
which is considered safe by experts (6).
The bacterial colonization of newborns by vaginal delivery or
cesarean section has been thoroughly studied in relation to the
immune system, the diet, the environment as well as many other
involved factors (1). Hospital staff, personal habits, infections,
stress, hormonal status, vaccination and agedness seem to be
crucial factors for the establishment of the bacterial microflora
which is actually called “microbiome” (1).
New technological applications have been brought into light.
Next generation sequencing (NGS) methodologies include
sequencing of the 16S ribosomal RNA gene (r RNA) as well
as metagenomic sequencing. Without any doubt technological
developments have empowered scientists with advanced
knowledge and stand for an in depth perception of the human
ecological communities of commensal, symbiotic and pathogenic
microorganisms. Microbes are able to participate in multiple
metabolic processes in our intestine, synthetizing and producing
key nutrients as well as repulsing pathogenic bacteria. To this
end, the “Human Microbiome Project” in the United States (US
National Institutes of Health, NIH, http://commonfund.nih.
gov/hmp/) (15) and the metaHIT Consortium (https://www.
gutmicrobiotaforhealth.com/metahit/) in Europe (16) have been
able to shed light on the composition of bacterial populations in
detail at the various human sites.
Without any doubt, diet is the major player of the microbiota
composition. Diet consists of introducing chemical substances
following consumption preferences in our intestinal ecosystem
in different timing (17,18). On another hand, host physiology,
immunological status and metabolism capacity regulate the
response to the bacterial colonization and the presence of specific
microbial species (1).
The Gut-associated lymphoid tissue (GALT) system sits in
the intestinal wall furnished by immunological elements able
to protect the intestinal wall from invasion. Malfunction of
the GALT following treatment by antibiotics, inappropriate
alimentation or stress leads to dysbiosis and increasing of the
intestinal permeability (1,19). GALT malfunction results in an
impaired immunity, either inefficient or exacerbated. Therefore,
infectious diseases as well as immune-mediated diseases (20,21)
such as allergy (22) and auto-immune (inflammatory) disorders
(23–25) may occurred following disruption of the equilibrium
between microbiota and host, the so-called dysbiosis. Along these
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Stavropoulou and Bezirtzoglou Probiotics in Medicine
lines, probiotics seem to be beneficial in these issues as they
stimulate the host immune system and preserve the microbial
intestinal balance via the barrier effect (1).
Probiotics seem to exert their effect through different
mechanisms (1,20) (Figure 1);
-Competition for space (Spatial arrangement theory) in the
intestinal lumen and wall (26,27).
-Antagonism between pathogenic bacteria and probiotics
which is produced by competition for nutrients found in
limited quantities in the intestine (26) or by pH modulation.
Maintenance of an acid pH on the epithelium by probiotics
(27,28).
-Synthesis of nutrients reported as sources for energy for
epithelial cells or bacteria (26).
-Maintenance of mucosal integrity. The intestinal
epithelium is part of the intestinal mucosa layer. This epithelium
is monolayer and the locus in between the epithelial cells is
tightly unified by transmembranar proteins. The intestinal
mucosa has 2 more layers, the lamina propria and the muscularis
mucosae, which bracket the epithelial monolayer. Probiotics
show a cytoprotective action upon the gastric mucosa integrity
by strengthening the epithelial junctions and preserving the
mucosal barrier function (29).
-Enhance intestinal barrier function. Preservation of the
microbial intestinal balance via the barrier effect (1).
-Regulation of gut motility (30). Intestinal motility as well
as reflexes and secretory functions of the gastrointestinal tract
are regulated by the Enteric Nervous System (ENS) found in
the intestinal wall. ENS is considered as a second brain as it
is composed of a complex neural network of sensory, motor,
inter neurons and glial cells. In this vein, there is a reciprocal
communication between Central Nervous System (CNS) and
bacterial flora in the intestine. The CNS affects the microbiota
by altering the motility and permeability of the gut or even via
mediators secreted by neuro-endocrine cells (30).
-Prevention of osteoporosis. Studies showed that
probiotic supplementation can both increase bone density
and protect against primary (estrogen-deficiency) and secondary
osteoporosis (31).
-Hypocholestaemic action (32). Hypocholestaemic effect
is bacterial species related. Different mechanisms have been
proposed. Deconjugation of bile acids (30), assimilation of
endogenous or exogenous cholesterol (33), binding of cholesterol
and free bile acids to the microbial cell (34) or co-precipitation of
the free bile acids (34).
-Anti-carcinogenic, antimutagenic and anti-allergic
activities (35–37). Studies in animals as well as cohort studies in
humans have demonstrated a correlation between consumption
of dairy products and the risk of colorectal cancer. Anticancer
activity of some strains is associated to the capacity of the
probiotic strain to inhibit or reduce DNA destruction in the very
first stages of carcinogenesis.
-Production of H2O2by probiotics promotes epithelial
restitution (38).
-Production of antimicrobial agents, organic acids and
bacteriocins (39–41) stimulates the production of intestinal
mucins which will prevent the implantation of pathogens.
-Their action on the intestinal immune system (1,42) by
stimulating the receptors of innate immunity, TLRs which will
cause the production of pro-inflammatory cytokines and lead to
the initiation of phagocytosis by macrophages.
Specifically, some probiotics induce activation of CD4
+and CD8 +T lymphocytes and secretion of IgA by
lamina propria plasma cells to neutralize pathogens, while
other probiotics suppress the Th1 inflammatory response and
the production of inflammatory cytokines IL-12, TNF-a, and
stimulate Treg lymphocytes (39). Therefore, they appear to have
a multifaceted role as an adjuvant to immunity or as a stifle of
inflammatory responses.
Undoubtedly antibiotics play a crucial role in the treatment
of infections, however their uncontrollable use has led to serious
ecological consequences but also for human health, as for
example the increase of multi-resistant strains and the alteration
of human floras and specifically of the intestinal microbiota and
its functions (5). In this vein, probiotics have been proposed as
a “non-invasive” alternative therapy or co-therapy to antibiotics.
As already stated, probiotics help to preserve the normal human
microbiota in a beneficial status.
FIGURE 1 | Mechanisms of action and properties of probiotics.
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Stavropoulou and Bezirtzoglou Probiotics in Medicine
According to WHO, probiotics are “living microorganisms,
which, when consumed in adequate amounts, have a health
benefit for the host.” Historically, Metchnikoff was the first
scientist to propose the use of probiotics. They may be used as
food supplements to consume or as medicines in the form of pills
or powder containing a single or a combination of several strains.
It is generally accepted that the dose of probiotic microorganisms
must be 100 million to 10 billion microorganisms for it to
be effective.
GASTROINTESTINAL DISEASES
Without any doubt, the strongest evidence supporting the use of
probiotics is related to the treatment of gastrointestinal diseases
and specifically the acute diarrhea.
Gastroenteritis
Probiotics are of scientific interest for intestinal pathology. Their
effects are reported in multiple clinical studies (Table 1).
Some strains of E. coli, as well as Salmonella spp., Shigella spp.,
Campylobacter spp. and viruses like Rotavirus, Norovirus etc
are among the most frequent causes of gastroenteritis leading to
inflammation of the intestine. Lactobacillus strains are the main
players of the commercially available probiotics. Lactobacillus
strains have been shown to be effective against the pathogens E.
coli and C. difficile (43).
Specifically, Lactobacillus F19 and L. reuteri have a positive
impact on the gastrointestinal microbiota by boosting the
immunological status (44,45). Similarly, Lactobacillus casei
(431strain) is boosting the immune response and contributes
on the faster convalescence of the diarrheal disease in children
(45,46). Streptococcus thermophilus and Bifidobacterium bifidum
(TH-4+BB12 strain) drop the risk of the Rotavirus diarrhea
and colic’s in children (46,47). Lactobacillus acidophilus (NCFM
strain) +Bifidobacterium lactis (Bi-07 strain) have a beneficial
effect on the gastrointestinal ecosystem by reducing abdominal
floating (48).
Antibiotic Associated Diarrhea and
Traveler’s Diarrhea
Lactobacillus GG,Enterococcus faecium (SF68 strain), and
Saccharomyces boulardii have a strong recommendation for
the prevention of antibiotic-associated diarrhea, the treatment
of C. difficile colitis, as well as treatment of gastroenteritis
in addition to oral rehydration therapy (49,50) (Table 1).
Saccharomyces cerevisiae variant boulardii CNCM I-1079 has
been given successfully to treat and prevent acute cases of
antibiotic-associated diarrhea and traveler’s diarrhea as described
(51,52). The same authors (51,52) observed that Lactobacillus
Rosell-52, Bifidobacterium Rosell-175 and Lactobacillus Rosell-
11 strains were able to prevent pathogen invasion and treat
traveler’s diarrhea.
Nevertheless, studies have shown that a Lactobacillus
acidophilus commercial strain acquired vancomycin resistance
of vanA genes from enterococci in the gastrointestinal tract of
germ-free mice in vitro and in vivo (69).
TABLE 1 | Use of probiotics in gastrointestinal disorders.
Disease state Probiotic References
Gastroenteritis -Lactobacillus (43)
-Lactobacillus F19 and L. reuteri (44,45)
-L. casei (431strain) (45,46)
-S. thermophilus and B. bifidum
(TH-4+BB12 strain)
(46,47)
-L. acidophilus (NCFM strain) +
B. lactis (Bi-07 strain)
(48)
Antibiotic associated
diarrhea and traveler’s
diarrhea
-Lactobacillus GG,E. faecium
(SF68 strain) and S. boulardii
(49,50)
-Saccharomyces cerevisiae
variant boulardii CNCM I-1079
(51,52)
-Lactobacillus Rosell-52,
Bifidobacterium Rosell-175 and
Lactobacillus Rosell-11
(51,52)
-L. reuteri DSM 17938 and L
acidophilus LB (low efficacy)
(53)
Clostridioides difficile
infection
-S. boulardii, Lactobacillus spp. (54–58)
Inflammatory bowel
disease
-Escherichia coli Nissle 1917 or
Lactobacillus GG
(59–63)
-Bifidobacterium spp. and
L. acidophilus
(59–63)
-S. boulardii (64)
-Lactobacillus GG and
L. johnsonii
(65)
Celiac disease -Bifidobacterium spp. and
L. acidophilus, various
(59–63,66)
Helicobacter pylori
infection
-Bifidobacterium BB-12 (67)
-L. acidophilus La-5 (13)
Lactose Intolerance -Lactobacillus delbrueckii
subspecies bulgaricus and
S. thermophilus
(68)
Similarly, we should note that the SF68 strain of Enterococcus
faecium is a possible recipient of the van A gene cluster
(70). Thus, Enterococcus faecium SF68 strain profile has led to
concerns about the safety of probiotics containing this strain (70).
Those studies underpin the issue of the potential health risk
when consuming probiotic foods containing enterococci which
could be potential recipient of glycopeptide resistance genes (70).
Following EFSA and the Panel on Additives and Products or
Substances used in Animal Feed (FEEDAP) (2008), Microbial
Inhibition Concentration(MIC) antimicrobials standards have
been designated for most common probiotics; Lactobacillus,
Streptococcus thermophilus, Pediococcus, Lactococcus,
Leuconostoc, Enterococcus, Bifidobacterium, Propionibacterium,
and Bacillus.
More studies bring into light that the glycopeptide resistance
of Lactobacillus strains is different from Enterococci and
underline the safety of Lactobacillus strains used as probiotics
with regard to their vancomycin resistance (71).
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Stavropoulou and Bezirtzoglou Probiotics in Medicine
L. reuteri DSM 17938 and L. acidophilus LB have a lower
recommendation (53). In a Cochrane’s study (72), the efficacy of
probiotics on acute infectious diarrhea in subjects of all ages was
studied and a reduction in the duration of diarrhea by 1 day was
demonstrated. There is no doubt that the evidence is weak and
the methodological limits are questionable.
Clostridioides difficile (Formerly
Clostridium) Infection Pseudomembranous
Colitis
As aforementioned, probiotics can be given as part of the
treatment of Clostridium difficile colitis (Table 1). We focus our
interest in this part during the last years; we notice an increase of
C. difficile cases worldwide, associated to the misuse of antibiotics
(54). The effect of administering probiotics on a Clostridium
difficile has been evaluated in several studies with questionable
results (73). A Swiss study finds that the action of probiotics
depends on the basic risk of patients (>5%) of developing post-
antibiotic pseudomembranous colitis (55,74,75).
C. difficile infection is a cause of post-antibiotic nosocomial
diarrhea, the so called pseudomembranous colitis. The infection
is due to gut microbiota alterations as a result of antibiotic
treatment or other causes of microbiome alterations such as
travel (76).
Clostridioides difficile and its spores are ubiquitous in the
environment and thus are able to colonize the human intestine
(74). The intestinal mucus appeared to be an important
chemotactic factor for colon colonization by Clostridium difficile
(55). Recently, the epidemics observed of Clostridium difficile
seem to be linked to extremely virulent clones of this anaerobic
bacterium in several countries; the genotypes 027 and 078 (77,
78). The infection could induce a toxic megacolon and lead to
intestinal perforation and septic shock (73). In Switzerland, the
disease is not obligatory reportable and only the clone 078 has
been isolated (74,75).
In a European global study on hospital strains, the ribotype
078 was the 11th most frequent ribotype in Europe. Of all 14
European countries enrolled in this study, Greece represented
>10% of the strains with the virulent ribotype 078 (54).
Moreover, in Greece, the hypervirulent genotype 027 has not
been found, whereas genotypes 017 and 126 predominate (79).
In Spain, the genotypes 078 and 126 predominate in patients
(80). Globally in Southern Europe (Greece, Italy, Portugal and
Spain), the genotypes 078 and 126 and 017 are the most common
dominating genotypes (77). The genotype 017 is also found in
Bulgaria and Poland (79).
It is of note that most patients having Clostridium difficile
infection have been exposed to longterm antibiotics suffer from
comorbidities and are elderly. It seems that the prevalence of the
disease is closely associated to the abuse of antibiotics, specifically
fluoroquinolones, cephalosporins as well as penicillins (78). Yet,
most of the cases are hospital acquired (64%) compared to the
community acquired cases (79).
The European Society of Clinical Microbiology and Infection
(ESCMID) (2009) issued treatment guidance for Clostridium
difficile infection (73), reviewing different treatment protocols
such as antibiotics, immunotherapy, toxin-binding resins
and polymers, probiotics, and fecal or bacterial intestinal
transplantation. Guidelines are specified following disease
state. Recommended antibiotics, are mostly vancomycin and
fidaxomicin and less metronidazole than it used to be. In
cases of recurrences fecal transplantation is recommended
in combination with oral antibiotic treatment. Probiotics
(Saccharomyces boulardii, Lactobacillus spp.) are also given in
combination with oral antibiotic treatment (54,56–58).
Probiotics (Saccharomyces boulardii, Lactobacillus spp.) can
also be given in combination with oral antibiotic treatment (55).
Although several studies showed a moderate evidence on
the beneficial effect of probiotic prophylaxis in C. difficile
diarrhea (56,57), a Cochrane study analysis suggests to
adjunct them to the antibiotic therapy in the treatment of
CDI (58). However, a study on the use of Saccharomyces
boulardii in immunocompromised patients showed occurrence
of invasive disease (81,82). Another study on probiotic use
as prophylaxis agent showed increased mortality due to non-
occlusive mesenteric ischemia (83).
Therefore, the ESCMID guidelines do not recommend
probiotics as an adjunctive treatment for CDI.
In consent with the European guidelines, the Infectious
Diseases Society of America (IDSA) together with the Society
for Healthcare Epidemiology of America (SHEA) issued similar
guidelines summarizing that due to lack of evidence probiotics
are not recommended (84).
Inflammatory Bowel Disease
Probiotics seem to have an effect on inflammatory bowel
disease (85,86) (Table 1). Studies on colitis animal models
show a decrease in inflammatory status and the expression of
inflammatory mediators.
Administration studies of the various probiotics remain
differentiated in terms of treatment effectiveness. While some
authors report that there is no difference in the relapse rate but
simply a longer interval without relapse for the treatment of
ulcerative colitis with probiotics such as Escherichia coli Nissle
1917 or Lactobacillus GG, others accept that supplementation of
medical treatment with Bifidobacterium spp. and L. acidophilus
improves clinical response (59–63). In addition, remission
seems to be observed in pediatric subjects after long-term
probiotic treatment as a supplement to medical treatment with
mesalazine (87). Administration of S. boulardii in combination
with mesalazine shows a considerable positive effect. Probiotics
have also been applied in the treatment of Crohn’s disease
(64). Fewer recurrences were observed after administration of
Lactobacillus GG and Lactobacillus johnsonii (65).
Pouchitis is the inflammation in the lining of a pouch as a
result of colorectal surgery. In this context, some researchers have
used probiotics for the treatment of active pouchitis inducing
remission in 69% of subjects (65,88), while other authors doubt
the efficacy of probiotics on the treatment of pouchitis (66).
Celiac Disease
To date, it is well known that gluten is the trigger in celiac disease.
Nevertheless, it is suggested that intestinal microbiota might play
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Stavropoulou and Bezirtzoglou Probiotics in Medicine
a certain role in the pathogenesis and progression of the disease
(66). Dysbiosis in the microbiota of patients with celiac disease
has been reported in some studies with an intestinal microflora
characterized by an abundance of Bacteroides spp. and a decrease
in Bifidobacterium spp. (66). This could suggest that probiotics
might have a beneficial effect on this condition (Table 1).
Other Intestinal Associated Pathology
Intake of Bifidobacterium BB-12 has an impact on Helicobacter
pylori infection in humans (67). Likewise, L. acidophilus La-5
also impacts Helicobacter pylori, boosts the immune effect and
alleviate diarrheal symptoms (13) (Table 1).
Treatment of Lactose Intolerance
Lactose intolerance is due to the inability to digest lactose
in dairy products. It is believed to affect 60% of the
world’s population (89). However, lactose malabsorption varies
considerably in the different countries from 5 to 15% in
Northern Europe and America to 50–100% in South America,
Asia and Africa. Lactobacillus delbrueckii subspecies bulgaricus
and S. thermophilus in yogurts improve the intolerance to
lactose as they possess the enzyme beta- galactosidase (68)
(Table 1). Recently, randomized double-blind studies showed the
efficiency of probiotic bacteria in fermented and unfermented
milk preparations given to alleviate the clinical symptoms of
lactose malabsorption (89).
ALLERGY
Allergy results from an exacerbated hypersensitivity response of
the immune system to usually harmless triggering substances in
the environment. These substances are called allergens and they
usually include drugs, foods, grass and tree pollen, insects, insect’s
bites and stings, dust mites, pet dander, chemicals and latex.
This hypersensitivity in immune system tolerance
mechanisms seems to be modulated by the gut microbiota
(90). Dysbiosis has been incriminated for the development of
allergies (91). Probiotics have been successfully used in the
treatment of allergic diseases such as allergic rhinitis, asthma,
atopic dermatitis and food allergy (90). However, there is still
controversy over their use.
Two meta-analyses reported improvement in the prevention
of atopic dermatitis by the use of probiotics (92,93). Lactobacillus
alone and Lactobacillus along with Bifidobacterium seem to
be protective against the development of atopic dermatitis,
specifically when given early in pre- and postnatal high allergy
risk populations as well as in the general population (93)
(Table 2).
Lactobacillus paracasei, Lactobacillus salivarius (LS01 strain),
and Lactobacillus fermentum are also used for the treatment of
atopic dermatitis as antiallergic in children (94,95). The use
of probiotics in allergic conditions such as atopic dermatitis is
promising (109).
Initially treatment was succeeded with a single probiotic
strain. Among Lactobacillus species the most common
in the therapy of allergic rhinitis are; Lactobacillus casei,
Lactobacillus rhamnosus, Lactobacillus johnsonii EM1,
TABLE 2 | Use of probiotics in allergy.
Disease state Probiotic References
Atopic dermatitis -Lactobacillus (93)
-Lactobacillus +Bifidobacterium (93)
-L. paracasei (94,95)
-L. salivarius (LS01) (94,95)
-L. fermentum (94,95)
Allergic rhinitis -L. casei, L. rhamnosus, L. johnsonii
EM1, L. acidophilus, L. gasseri, L.
paracasei
(96–99)
- B. lactis NCC2818 (Nestle) (100)
-L. paracasei (LP-33 strain) (101)
-Lactobacillus GG (LGG) +L. gasseri,
L. acidophilus+Bifidobacterium lactis
(102–104)
- VSL#3 (4 Lactobacillus+3
Bifidobacterium+1 Streptococcus
thermophiles)
(102–104)
-Lactobacillus+Bifidobacterium (105)
-L. casei (106)
Atopic eczema -Bifidobacterium BB-12 (90,107,108)
-B. longum, B. clausii,E. coli Nissle
(EcN) 1917
(90,107,108)
Lactobacillus acidophilus,Lactobacillus gasseri,Lactobacillus
paracasei (96–99).
As stated previously, Bifidobacterium BB-12 alleviate
symptomatology of the atopic eczema.
Bifidobacterium longum,Bacillus clausii, and Escherichia coli
Nissle (EcN) 1917 are also used as pharmatherapeutics (107,108).
The use of Bifidobacterium lactis NCC2818 (Nestle) as well as
Lactobacillus paracasei (LP-33 strain) seems to reduce the severity
of the symptoms of allergic rhinitis (100,101).
Recently, combination treatment was made possible with
more than one probiotic strains. Lactobacillus GG (LGG) +
L. gasseri, L. acidophilus +Bifidobacterium lactis and also
the commercial mixture VSL#3 consisting of 4 lactobacilli+3
bifidobacteria+1 Streptococcus thermophilus were used
combined (102–104).
The combination of Lactobacillus +Bifidobacterium in
treatment seems to be the most popular and successful for the
allergic rhinitis (105).
Lactobacillus casei administered in children with mite allergies
decreased the frequency and severity of symptoms (106).
Studies on the role of probiotics in prevention or treatment of
food allergies were conducted but with contradictory results (90,
110). Heterogeneity of strains, duration and dosage of treatment
should probably explain some of the differences.
RESPIRATORY DISEASES
Asthma
A raise in asthma and respiratory diseases has been observed
during the last years in most industrialized countries (111).
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TABLE 3 | Use of probiotics in respiratory diseases.
Disease state Probiotic References
Asthma Enterococcus faecalis FK-23 (113)
Cystic fibrosis -Various (114–118)
Respiratory infections
(global)
L. rhamnosus GG (119)
L. reuteri DSM 17938 (120)
L. reuteri ATCC 55730 (121)
As formerly discussed, the gut microbiota plays a capital role
in the development of allergic diseases.
The modulation of the normal gut microbiota in an
experimental model of asthma in animals has been registered
(112). Children at risk of asthma showed microbial dysbiosis
in their intestine with complete absence of certain bacterial
genera (112). Hence, the administration of these “missing
bacteria” in models of mice showed a decline in respiratory
tract inflammation indicating their potential role as a causal
agent in asthma (112). Recently, there appeared evidence
that Enterococcus faecalis FK-23 suppresses the asthmatic
hypersensibility which seems to be associated with attenuation
of Th17 cell development (113) (Table 3).
However, meta-analyses and double-blind randomized
controlled studies did not perceive any substantial benefit from
probiotic treatments (122–124).
Cystic Fibrosis
Cystic fibrosis is an autosomal recessive disorder caused by
a mutation in the CF transmembrane conductance regulator
(CFTR) gene encoding the CFTR protein which regulates the
movement of chloride and sodium ions across epithelial cell
membranes. The result is a defective ion transport with a buildup
of thick mucus throughout the body, leading to respiratory
insufficiency, along with many other systemic disorders, mostly
digestive. Moreover, the decreased mucociliary clearance in the
respiratory tract, combined to the defective ion transport allows
the proliferation of Pseudomonas aeruginosa as well as other
pathogens in the respiratory tract which become more and more
resistant due to iterative treatments and result in a repetitive
inflammatory response (114).
Other than chronic respiratory disease, cystic fibrosis
is associated, as aforementioned with digestive disorders
(pancreatic, biliary and intestinal) also resulting in chronic
inflammation as well as malabsorption of nutritious substances.
Probiotics seem to be promising for certain respiratory tract
diseases including cystic fibrosis (115) (Table 3). In the case of
cystic fibrosis there is a dysbiosis and frequent antibiotic therapy
is able to unbalance the microbiota (116). In this context, the use
of probiotics has been studied as it appears that they may reduce
the rate of pulmonary exacerbations in the disease (117,118).
Respiratory Infections and COVID-19
L. rhamnosus GG reduces the risk of respiratory and
gastrointestinal infections in infants (119).
Viral respiratory infections affect morbidity and mortality of
a population. Pattern recognition receptors (PRRs) are the main
sensor players of the innate immune response. Expression of
many Pattern Recognition Receptors (RRs) is exacerbated in
the lung cells during inflammation. In this vein, macrophages,
monocytes, neutrophils are responding by increasing levels of
PAMPs (Pathogen-Associated Molecular patterns) and DAMPs
(Danger-Associated Molecular Patterns) (125).
It is known that intruder’s pathogens have a specific unique
profile of PAMPs resulting in a specific immune response (126).
PAMPs are necessary molecules for the pathogens survival; hence
they are not produced by the host. In viruses, the major PAMPs
are nucleic acids or glycoproteins. PAMPs should be recognized
by PRRs conducting to the expression of cytokines, chemokines,
and other co-stimulatory molecules in order to eliminate the
pathogenic virus and activating then antigen presenting cells and
specific adaptive immunity (127,128). The most studied PRRs for
pathogens recognition are TLRs (Toll Like Receptors) which are
membrane glycoproteins (129).
Without any doubt, there is a clear diversity in the patterns for
pathogen recognition and host protection upon viral infections.
On the other side, PRRs recognize DAMPs (Danger-
Associated Molecular Patterns) as danger signals released by
damaged or necrotic host cells which reinforce the pro-
inflammatory response (130). As a result, stimulation of TLRs is
crucial for the protection from the development of diseases.
Probiotics’ regulatory effect on the expression of Toll-
like receptors (TLRs) was observed in several disease cases
(131). Specifically, probiotics impede or reduce inflammation
by minimizing the expression of TLR4 (132). In this vein, a
large randomized controlled trial was conducted (PROSPECT
Investigators and the Canadian Critical Care Trials Group) for
the use of probiotics in critically ill patients of intensive care units
(ICU) with ventilator-associated pneumonia (VAP) showing
beneficial and salutary effects of probiotics in this seriously ill
patients (133).
Although, it has long been known that Coronaviruses
cause respiratory and sometimes gastrointestinal diseases with
mostly like clinical presentations, the SARS-CoV-2 has recently
monopolized our interest due to the COVID-19 pandemic as a
result of its contagiousness as well as unexpected mortality rates.
Coronaviruses are recognizably different than most enveloped
viruses in nature as they are localized in the lumen of the ERGIC
(ER-Golgi intermediate compartment). The ERGIC mediates
between the endoplasmic reticulum and the Golgi on the
secretory pathway for releasing of the infectious virions from the
infected cell (134). This is where the majority of the E protein
is localized, participating in the assembly and budding of the
infectious virion.
It is known that virus replication in the host for establishment
of an infection occurs through host-viral PPIs (Protein-protein
interactions) (135,136). In SARS-CoV-1, The E protein has only
been mentioned to connect to five host proteins (Bcl-xL, PALS1,
syntenin, sodium/potassium (Na+/K+) ATPase α-1 subunit, and
stomatin) (135).
Latest information states that Coronaviruses encode PBM-
containing proteins that bind to cellular PDZ proteins. Those
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TABLE 4 | Use of probiotics in neurological and psychiatric diseases.
Disease state Probiotic References
Neurological and psychiatric
diseases
-L. rhamnosus (142–144)
Autism Spectrum Disorder
(ASD)
-L. acidophilus Rosell-11
-Various
(145–147)
Autoimmune myasthenia
gravis
Various (148)
Autoimmune
encephalomyelitis
Various (149)
proteins keep an important role in the anchoring receptor
proteins (135). Alongside, E protein interaction partners are
identified as p38 mitogen-activated protein kinase (MAPK)
inhibitors. Clearly, this is an important therapeutic tool as studies
have shown that inhibitors of p38 mitogen-activated protein
kinase (MAPK) prolonged survival in mice (137,138).
Lactobacillus contains a HSP27-inducible polyphosphate
(poly P) fraction. Probiotic-deriving polyphosphates have
the ability to strengthen the epithelial barrier function and
keep intestinal homeostasis through the integrin-p38 MAPK
pathway (139).
As most treatments targeting Coronaviruses are currently
ineffective, bringing into light more interaction partners for
Coronavirus protein E could enhance a therapeutic approach.
L. reuteri DSM 17938 showed beneficial effects against upper
respiratory tract and gastrointestinal symptomatology (120).
Similarly, L. reuteri ATCC 55730 has been shown to alleviate
respiratory tract and gastrointestinal symptomatology in workers
in Sweden (121).
During the last years, the gut–lung axis in bacterial and viral
infections is considerably discussed (140). It seems that intestinal
microbiota amplifies the alveolar macrophage function (140) and
as a result, gut microbiota acts as a protective mediator during
pneumonia (141).
We state here the importance to clarify the involved
mechanisms of the probiotic efficiency in respiratory diseases
which could potentialize their use as prophylactic or field therapy.
In conclusion, more knowledge is necessary to define the
role of probiotics as therapeutics in viral and other respiratory
diseases, as we have as yet only scratched the tip of this
complicated issue.
NEUROLOGICAL AND PSYCHIATRIC
DISEASES
During the last years, there is increasing interest in the
use of probiotics for prevention and treatment of neurologic
diseases (Table 4). Recent studies stated the potential role
for microbiota in the pathogenesis of neurological and brain
disorders (150–152).
It is believed that there is reciprocal communication between
the central nervous system and the intestine, the so-called
“microbiota-gut-brain axis” (150,152). which is a model of
interaction between the intestinal microflora and the brain.
Physical and psychological stress may interfere in the control
of the intestinal and the vaginal microflora. Higher numbers of
the putrefactive bacteria Clostridium sp are found under stress
(153,154).
Early-life events such as stress, environmental factors or other
may impact the intestinal microbiota (155).
Studies report that the ingestion of Lactobacillus rhamnosus
regulated the transcription of γ-aminobutyric acid (GABA)
receptors and therefore emotional behavior (154). The intestinal
microbiota affect GABA which transmit signals to the brain
trough enteric nerve s (142).
Normal microbiota preserves the intestinal balance by
improving epithelial tight junctions reducing gut permeability
(150).Otherwise, in case of cellular damage, multiple immune
and inflammatory responses are produced as well as activation
of the spinal neurons and the vagus nerve (156). As a result,
inflammatory cytokines are produced affecting the central
nervous system (156).
Autism spectrum disorder (ASD) is a developmental disability
that can cause problematic behavior in social, emotional, and
communication skills. It seems that there is a connection between
gut bacteria and autism (145,146).
Taking the above into account, we understand the
pivotal role of the gut microbiota in the neural and brain
development and regulation and general and mental health
affection in case of imbalance. Maternal feeding plays an
important role in gut microbiota of the newborn (1), as it
contains probiotics.
Studies showed potential effects of probiotics in the treatment
of neurologic diseases (143) (Table 4).
Positive effect of probiotics have been observed in the
progression of the autoimmune myasthenia gravis (148),
the autoimmune encephalomyelitis (149), as well as on
motor behaviors (144). Moreover, probiotics seem to have
neuroprotective properties (157) and a positive impact on
cognition (158).
Improvement of the antisocial behavior, communication and
concentration problems was observed in a cohort study of
children with ASD treated with the probiotic strain L. acidophilus
Rosell-11 during a period of 2 months (147).
Probiotics have been studied in the treatment of the above
neurological diseases. However, the current evidence on their
efficacy is poor. As already discussed, their efficiency is strain,
tissue, and dose dependent.
Studies undertaken are not uniform in terms of the chosen
characteristics of the population, the population size, the
undertaken therapies and procedures and the suitable strain or
strains’ mixture.
Rare cases of adverse effects of probiotics have been
observed (159). It is also notable to state that immaturity of
the neurological system, mental retardation and other severe
neurodevelopmental problems predispose those patients at
potentially higher risk of adverse effects.
Without any doubt, when the mechanisms of action of the
probiotics are completely understood, we would then be able
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to evaluate their safety and efficiency issues on neurological
diseases (140).
LIVER DISEASES AND HEPATIC
ENCEPHALOPATHY
There is mutual communication between the central nervous
system and the liver, the so-called “microbiota-gut-liver axis.”
Thereby, there is a reciprocal interaction between hepatic
receptors (Toll-like receptors) and bacterial lipopolysaccharides.
When intestinal imbalance occurs prompting the alteration of the
intestinal permeability, immune and inflammatory responses are
produced and can result in hepatic disorders. Moreover, nutrients
absorbed by the gut reach the liver.
Cirrhosis seems to be associated with changes in the presence
of Bifidobacterium species in the intestinal microbiota (160).
Moreover, modifications of the intestinal microbiota have
been observed among patients with chronic hepatitis B
(161), primary sclerosing cholangitis (160) and proliferation of
hepatocellular carcinoma (161). There was diversity observed in
intestinal microbiota amongst subjects with hepatitis B virus-
related cirrhosis and subjects with chronic hepatitis B (160,161).
Hepatic encephalopathy is closely related to the intestinal
microbiota (162). The metabolic activity of the intestinal
microbiota on amino-acids results in the production of toxic
substances (NH3, phenols, amines, phenolic acids) that are
inactivated in the liver. However, when liver failure occurs these
substances are not inactivated, they enter the circulation, cross
the hematoencephalic barrier and cause hepatic encephalopathy
resulting in coma.
The mainstay of treatment of hepatic encephalopathy is
lactulose and lactitol, laxative agents that can be considered
as prebiotics as they lower blood ammonia concentrations,
possibly by favoring colonization with acid-resistant, non-urease
producing bacteria. Moreover, they also act by altering the
colonic pH, improving gastrointestinal transit and increasing
fecal nitrogen excretion (163).
In this same spirit, probiotics have also been proposed as an
adjunctive treatment for hepatic encephalopathy.
Lactic acid bacilli, more specifically Lactobacilli and
Bifidobacteria seem to be the most effective species for
hepatic encephalopathy but Clostridium butyricum,Escherichia
coli Nissle 1917, Streptococcus salivarius, and Saccharomyces
boulardii are also used (164) (Table 5).
TABLE 5 | Use of probiotics in Liver diseases.
Disease state Probiotic References
Cirrhosis Bifidobacterium sp. (160)
Hepatic encephalopathy -Bifidobacterium sp., Lactobacillus
sp., C. butyricum, E. coli Nissle 1917,
S. salivarius, S. boulardii
(164)
- C. butyricum, B. infantis (162,165)
Treatment with the probiotics Clostridium butyricum and
Bifidobacterium infantis seems to be promising as an adjuvant
therapy for the management of the mild hepatic encephalopathy
(162,165).
According to a meta-analysis of 21 trials, when compared
to placebo/no treatment, probiotics seem to be beneficial in
treatment of hepatic encephalopathy but do not seem superior
compared to lactulose (165).
Other than the treatment of hepatic encephalopathy,
probiotics have also been studied as prophylaxis to prevent
recurrence with beneficial effects (166).
Based on the fact that changes in gut microbiota are inducing
liver diseases, an increasing interest in regulating the gut
microbiota by probiotics for the treatment of liver disorders is
reported (167). However, the current evidence on this efficacy
is unclear. As stated previously, the efficiency of a probiotic is
strictly strain, tissue, and dose dependent.
It is necessary to proceed to high-quality randomized
clinical trials with standardized procedures on the undertaken
probiotic therapy with appropriate strains and diligent choice
of the population size and characteristics in order to get
knowledge on the efficacy and safety of probiotics. In these
terms, probiotics cannot be recommended for the treatment
of most hepatic disorders, aside from some implication on
hepatic encephalopathy.
GENITO-URINARY INFECTIONS
Bacterial vaginosis is a vaginal inflammation caused by an
imbalance of the vaginal flora with overgrowth of several bacterial
species and decrease in Lactobacilli. It seems that women at
reproductive age develop more frequently vaginosis.
Historically, Albert and Döderlein in 1892 stated the
importance of the vaginal flora in women’s overall health (168).
Lactobacillus spp. and specifically the species L. crispatus are
predominant in the bacterial flora of healthy women (169).
As known, Lactobacillus spp produce lactic acid protecting the
vagina from colonization by pathogens. However, when the
TABLE 6 | Use of probiotics in Genito-Urinary tract infections.
Disease state Probiotic References
Bacterial vaginosis -Lactobacillus spp. (169)
-L. crispatus (169)
-L. acidophilus (170,171)
-L. rhamnosus GR-1 (170,171)
-L. fermentum RC-14 (170,171)
Gardnerella vaginalis -Lactobacillus spp. (172)
-L. acidophilus (172)
Urinary tract infections
(UTIs)
-Lactobacillus rhamnosus GR-1 (173)
-L. reuteri RC-14 (173)
-L. casei Shirota (173)
-L. crispatus CTV-05 (173–175)
-L. rhamnosus GG (173)
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balance is disturbed and Lactobacillus are decreasing or missing
vaginosis occurs.
In this vein, scientists have tried to restore this imbalance of
the vaginal flora by oral or vaginal administration of lactobacilli
(170,171) (Table 6).
L. acidophilus seems to have a positive effect in prevention and
treatment of bacterial vaginosis (171,176).
However, the mechanism of action of Lactobacillus remains
unclear. While some scientists claim that the production of lactic
acid inhibits the establishment of pathogens by creating an acid
environment (1), in vitro studies have stated that the production
of H2O2or bacteriocins by certain Lactobacillus protects against
pathogens involved in bacterial vaginosis (176,177). Thus, the
adherence of Gardnerella vaginalis to the vaginal epithelium is
inhibited by Lactobacillus strains (172). Studies have shown that
the bacteriostatic effect of L. acidophilus on G. vaginalis NCTC
11292 dropped by 60% when culture pH turned to alkaline by the
addition of NaOH or by catalase denaturation of the H2O2(172)
(Table 6).
Moreover, it seems that administration of L. acidophilus or
Lactobacillus rhamnosus GR-1 and Lactobacillus fermentum RC-
14 for an extended period of 2 months is beneficial in the
vaginosis treatment (170,171).
In conclusion, probiotics can be effective in preventing
and treating vaginal imbalance in bacterial vaginosis. Studies
undertaken are encouraging. More research and clinical studies
are necessary in order to define whether or not probiotics are
efficient for the prevention and treatment of vaginosis and which
strains should be involved.
Urinary tract infections (UTIs) are among the most common
infections. Shortness of the women urethra is associated
with more frequent urinary tract infections in women. They
are divided in uncomplicated and complicated and include
cystitis, pyelonephritis, febrile UTIs, prostatitis and urinary-
source bacteriemia. UTIs mostly result when uropathogens,
mostly from the fecal flora, ascend the urinary tract or from
seeding of the kidneys via bacteremia or following medical
interventions (urinary catheters, urological surgery). Clinical
presentations vary from asymptomatic bacteriuria to urethritis,
cystitis, prostatitis, pyelonephritis and bacteriemia.
UTIs are associated with an important economic impact due
to many hospitalisations as well as morbidity, mortality and most
importantly development of microbial resistance (178–180).
Development of multi-drug resistance has led doctors to look
for milder prophylactic therapies in order to minimize the high
cost of therapies (181).
Probiotic effects on urinary tract infections remain
controversial (181–183) (Table 6). While a team states that
there is no benefit from probiotics administration (182), other
scientists observe a shortening of the average duration of
illness, as well as a considerable reduction of the infection rate
(181,184).
An extended review based on a search of PubMed for relevant
articles showed the efficacy and safety of probiotics as prophylaxis
against potential pathogenic bacteria of the urinary tract (185).
Lactobacillus rhamnosus GR-1 and L. reuteri RC-14 seemed to be
the most effective probiotic strains followed by L. casei Shirota
TABLE 7 | Use of probiotics in metabolic syndrome and cardiovascular diseases.
Disease state Probiotic References
Diabetes -Lactobacillus (188)
-Bifidobacterium (188)
-Various (189–191)
Obesity -Various (175)
Cardiovascular disease and
cholesterol
-Lactobacillus (41,188–192)
-Bifidobacterium (41,188–192)
-Various (41,183,188–
190,192)
and L. crispatus CTV-05 (185). The effectivity of L. crispatus in
UTIs has been observed by many authors (186,187).
On the contrary, L. rhamnosus GG is not shown to be
sufficiently effective (185). It seems that probiotics’ activity and
efficiency is closely related to the specific administered strain.
Hence, all authors agree on the safety issue of their use (185).
METABOLIC SYNDROME AND
CARDIOVASCULAR DISEASES
Diabetes
The gut microbiome seems to play a role in the development
of diabetes. Studies in animals have shown that some species of
Lactobacillus and Bifidobacterium could prevent or reduce the
severity of type 2 diabetes (188) (Table 7).
Studies in humans have attempted to assess the
factors that justify metabolic changes, oxidative stress and
inflammation (188).
Lactic acid bacteria show antioxidant activity. Diabetic
subjects are characterized by constant systematic inflammation
with high levels of proinflammatory cytokines [TNF-a, IL-6,
b kinase inhibitor (IKKb), and Jun N-terminal kinase (JNK)]
which exert a negative effect on insulin. Lactic acid bacteria have
positive clinical effects on the treatment of specific populations
with type 2 diabetes by modulating the inflammatory status.
A meta-analysis of 12 randomized controlled trials showed
that probiotics considerably improved the fasting plasma glucose
(FPG) and the glycosylated hemoglobin (HbA1c) in type 2
diabetes (189). Similarly, the role of probiotic supplementation
in persons developing type 2 Diabetes Mellitus (T2DM)
in improving glycemic control showed an overall beneficial
effect (190).
Our body is exposed to different physico-chemical or
pathological conditions having as outcomes the production
of free radicals (ROS) which causes the oxidation in the
human cell. Hence, it has developed endogenous antioxidant
mechanisms to keep the homeostasis. Oxidative stress is
occurring when imbalance between free radicals (ROS) and
antioxidant mechanisms are taking place (193). In the case of
diabetes, disorders in lipid peroxidation, enzymatic systems as
well as impaired glutathione metabolism are observed.
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Pathogenesis of diabetes is then characterized by a potent
oxidative stress, as increased levels of reactive oxygen species
(ROS) are present (194).
The consumption of yogurt with live probiotics seems to touch
up the antioxidant status and fasting plasma glucose (FPG) levels
in type 2 diabetic patients (191).
OBESITY
The significance of the human gastrointestinal microbiota is
stated in the case of obesity as well.
Obesity is linked to structural and functional changes in the
gastrointestinal ecosystem. The intestinal microbiota of obese
patients is characterized by increased numbers of bacteria of the
phylum of Bacteroidetes. Low numbers of bacteria of the phylum
of Firmicutes are observed.
Diversity and abundance of certain bacterial populations can
trigger metabolic pathways leading to obesity (173).
Obesity is an important risk factor for type 2 Diabetes
mellitus and cardiovascular diseases due to the high levels
of inflammation mediators which (39) are recorded in obese
persons. Administration of probiotics and antibiotics - has been
used to stimulate weight gain in farm animals (3,40). However,
there is controversy in their efficacy by authors (174).
In humans, probiotics supplementation seems to decrease
values of metabolic parameters and leads to the reducing of the
weight gain in obese adults (175) (Table 7).
Lactobacillus spp. are associated with weight gain in children
treated for diarrhea (195). Without any doubt more research is
needed for estimating the role of probiotics in obesity.
CARDIOVASCULAR DISEASE AND
CHOLESTEROL
Cardiovascular diseases are a pivotal cause of death in the
western world.
Multiple studies in animal and humans have demonstrated
an important correlation between cholesterol levels and the
risk of coronary heart disease. Dietary interventions suggest
lowering of fat (low-saturated-fat diets) for the prevention of
cardiovascular disease.
Supplementation of diet with fermented dairy products
containing lactic acid bacteria seems to be in lowering blood
cholesterol alleviating the cardiovascular disease (Table 7).
In this context, Bifidobacterium spp. and Lactobacillus
spp. have been studied as food supplements with very
promising effects.
However, the mechanisms of action of the
antihypercholesterolemic potential of probiotics are yet
under study. Several scientists propose a cellular pattern,
which includes the binding of cholesterol to cellular surfaces
and/or cholesterol assimilation by growing cells and cholesterol
incorporation into the cellular membrane (196). Others rather
accept a chemical pattern which comprises the deconjugation of
bile via bile salt hydrolase, the coprecipitation of cholesterol with
TABLE 8 | Use of probiotics in cancer and cancer cellular lines.
Disease state Probiotic References
Tumor cell apoptosis -L. casei (199)
-B. longum (199)
-L. acidophilus (199)
Inhibition of human colon
cancer cell lines including
HT-29, SW 480, Caco-2
B. adolescentis SPM0212 (200)
Anti-proliferative and
pro-apoptotic effects in
human gastric cancer cells
and colonic cancer cells
-L. paracasei IMPC2.1 (201)
- L. rhamnosus GG (201)
-L. acidophilus 606 (202)
- LGG/Bifidobacteriumanimalis
subsp. lactis
(203)
Antitumor activities -Bacillus polyfermenticus (204)
-L. acidophilus NCFB 1748 (205)
deconjugated bile (192) or the production of short-chain fatty
acids by oligosaccharides (41).
CANCER
Gastrointestinal (GI) cancers are a major health problem,
accounting for 20% of all cancers and 9% of all causes of cancer
death in the world (197).
The role of the human intestinal microflora has been
extensively discussed in cancer disorders. Microbiota
imbalance seems to be linked to cancer. One of the most
representative examples is the correlation between S. bovis/S.
equinus complex infection and intestinal cancer, principally
colorectal (198).
Functional foods and probiotics seem to have a
protective role against cancer development (Table 8)
and also reduce the incidence of the post-operative
inflammations (206).
As shown by some investigators, probiotics possess
anti-proliferative and pro-apoptotic properties against
gastrointestinal cancers (207,208) (Table 8).
Similarly, milk fermented with Lactobacillus casei,
Bifidobacterium longum, and L. acidophilus showed beneficial
effects on tumor cell apoptosis (199).
Moreover, in cellular lines it has been observed that
Bifidobacterium adolescentis SPM0212 inhibited the proliferation
of three human colon cancer cell lines including HT-29, SW 480,
and Caco-2 (200) (Table 8).
Anti-proliferative and pro-apoptotic effects of Lactobacillus
paracasei IMPC2.1 and L. rhamnosus GG strain have been
observed in both human gastric cancer cells and colonic cancer
cells (201) (Table 8).
Furthermore, antitumor activities have been shown by Bacillus
polyfermenticus (204).
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TABLE 9 | Use of probiotics in osteoporosis.
Disease state Probiotic References
Osteoporosis -Various (31)
In addition, L. acidophilus 606 (202), and
LGG/Bifidobacterium animalis subsp. lactis (203)
have also shown activity against human colon
cancer cells.
L. casei Shirota is reported to prevent intestinal dysbiosis and
having an effect on bladder cancer by lowering fecal enzyme
activity (205). Lowering of fecal enzyme activity has also been
observed by L. acidophilus NCFB 1748 which decreases cancer
risk and radiotherapy-related diarrhea (205).
Nevertheless, most of the above studies were performed
in vitro, in cellular lines or in animal models displaying the
efficiency of probiotics in gastrointestinal cancers. As stated
previously, those studies ascribe in probiotics properties such
as, anti-carcinogenic effect, anti-mutagenic effect, derangement
in differentiation process in tumor cells, modifications of tumor
gene-expressions, inhibition of pro-carcinogenic bacteria and
improvement of the immune system and intestinal balance (206).
However, the mechanisms inducing these effects are not
completely understood. It is of paramount interest to expand
these studies in humans with specific clinical trials which could
strengthen our knowledge of the potential probiotic strain related
efficiency and safety, as well as of the administration procedure
and dosage for the different types and stages of cancer (206).
OSTEOPOROSIS
Human and animal studies indicated that probiotic
supplementation may be a therapeutic tool to the prevention
and treatment of bone loss as they strengthen bones and
skeleton (31). Moreover, probiotics protect against primary
estrogen-deficiency and secondary osteoporosis (31) (Table 9).
ORAL DISEASES
Gingivitis is an inflammation confined to the gingiva, while
in periodontitis the inflammation process affects all peridental
tissues and the alveolar bone.
P. gingivalis, A. actinomycetemcomitans, T. forsythia,
Staphylococcus intermedius, Candida albicans, and T. denticola
are the main pathogens associated to periodontitis.
Lactobacillus salivarius WB21 modulates the oral microbiota
and reduces risk of gingivitis and periodontitis (209) (Table 10).
Chewing gums or lozenges with probiotics can improve
periodontal disease (214).
Dental caries is tooth decay due to acids made by bacteria.
Following excess of sucrose, Streptococcus mutans found in
the oral cavity are able to adhere to the teeth enamel
causing demineralization of the tooth enamel. Probiotics can
reduce levels of Streptococcus mutans. It is reported that
TABLE 10 | Use of probiotics in oral diseases.
Disease state Probiotic References
Gingivitis -L. salivarius WB21 (209)
Periodontitis -L. salivarius WB21 (209)
Dental caries -L. reuteri (210)
-Various (211)
Halitosis -Various (212)
Oral candidiasis -L. rhamnosus GG (213)
TABLE 11 | Use of probiotics in autoimmune diseases.
Disease state Probiotic References
Sjogren’s syndrome -Various (215)
Rheumatoid arthritis -Various (23,216)
Systemic lupus erythematosus -Various (23,216)
Multiple sclerosis -Various (23,216)
systematic yogurt and fermented by Lactobacillus reuteri bovine
milk consumption for 2 weeks reduces Streptococcus mutans
population in the oral cavity by up to 80%(210) (Table 10).
Moreover, fluid or lozenges containing probiotics reduce
Streptococcus mutans levels (211).
Halitosis (Chronic bad breathing) is the unpleasant breath
odor attributed to the production of volatile sulfur compounds
especially during the mornings due to poor oral hygiene or dental
caries, periodontitis and other oral conditions. Reduction of the
volatile sulfur compounds is observed by H2O2produced by
probiotics. Additionally, probiotics compete for colonization in
the oral cavity (212) (Table 10).
Lastly, oral candidiasis (oral trush) is an opportunistic
mycosis, due to colonization of the mucous membranes of the
oral cavity mostly by C. albicans on the mucous membranes of the
oral cavity. Candidiasis occurs when the normal oral microbiota
balance is disturbed in immunocomprised patients, elderly or
patients receiving long antibiotic regimens. L. rhamnosus GG
seems to reduce the prevalence of C. albicans which is a normal
component of our oral microbiota (213) (Table 10).
AUTOIMMUNE DISEASES
Dysbiosis is linked to the pathogenesis of Sjogren’s autoimmune
syndrome (215) as a possible interaction between the human
microbiome and the clinical manifestations of the disease seems
to exist. All the same, if the human microbiome is revealed to play
a key role in the pathogenesis of Sjogren’s disease (215), the next
step could be new and promising therapeutic approaches such
as the administration of probiotics as an adjunctive treatment to
immunosuppressive therapy (Table 11).
Randomized controlled trials have shown promising
results in modulating beneficially human microbiota in
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Stavropoulou and Bezirtzoglou Probiotics in Medicine
TABLE 12 | Use of probiotics as vaccine adjuvant.
Disease state Probiotic References
Vaccine adjuvant Lactobacillus casei
431
(217,218)
Adjuvant to flu vaccine Lactobacillus
fermentum strain
VRI 003 (PCC)
(217–219)
autoimmune diseases such as rheumatoid arthritis, systemic
lupus erythematosus and multiple sclerosis (23,216) (Table 11).
VACCINE ADJUVANT
Lactobacillus casei 431 was used for boosting the immune
response and Lactobacillus fermentum strain VRI 003 (PCC) as
an adjuvant to flu vaccine and athletic endurance (217,218)
(Table 12).
Probiotics were shown effective in increasing immunogenicity
levels by auctioning upon seroconversion and seroprotection
rates in adults inoculated with Influenza vaccines (219)
(Table 12).
DISCUSSION
The normal microbiota of the intestine plays a very important
role in the body’s defenses (1) and in the occurrence of multiple
diseases such as, infections, autoimmune and allergic diseases
and other (218–222). Probiotics seem to be a modern approach
to prevent and reduce the symptoms of these diseases or as
an adjuvant therapy by maintaining the proper balance of our
intestinal microbiota (114).
A plethora of commercial products with differences in
strain(s) composition and potentiality have been developed
as probiotics and functional foods; Align B. infantis (4
mg/capsule ¼ 1 billion CFU), Activia yogurt (B. lactis;
100 million bacteria per gr), Culturelle (L. rhamnosus GG
(L. rhamnosus:10 billion bacteria plus insulin 200 mg per
capsule), Culturelle for kids (L. rhamnosus:1.5 billion bacteria
per packet), Florajen (L. acidophilus: 20 billion bacteria per
capsule), Florastor S. boulardii lyo: 250 mg per capsule), Howaru
(L. acidophilus/B. lactis: 10 billion bacteria per capsule), Kefir
(L. lactis. L. rhamnosus, L. plantarum, L. casei, L. acidophilus,
L. reuteri, Leuconostoc cremoris, Streptococcus diacetylactis, S.
florentinus, B. longum, B. breve, B. lactis: 7–10 billion CFU per
cup), Lactinex (L. acidophilus, L. bulgaricus: 106 CFU/tablet
and 109 CFU/packet), RepHresh Pro-B (L. rhamnosus,
L. reuteri: 5 billion CFU per capsule; vaginal use),VSL#3
(L. acidophilus, L. plantarum, L. paracasei, L. bulgaricus, B. breve,
B. infantis, B. longum, S. thermophilus: 225 billion bacteria per 2
capsules), Yakult (L. casei: 8 billion bacteria per 80 mL bottle),
Ultralevure (Saccharomyces boulardii CNCM I-745: 250,00 mg,
50 mg/cap) (223).
Adverse effects (224) of probiotics have been reported such as
abdominal cramps, loose stools, bloating, gas and flatulence.
Moreover, as probiotics are “living organisms,” their use is not
recommended in immunocompromised patients, such as those
receiving corticosteroid therapy and other immunosuppressive
treatment, transplanted and oncological patients especially those
undergoing chemotherapy. Besides, probiotic treatment is not
recommended in patients with prosthetic valves as there have
been reports of infective endocarditis due to probiotics (225).
It is also important to have a deep understanding of the role
of CYP enzymes (226). CYP enzymes represent a superfamily
of enzymes that play an important role in the process of
activating or inactivating a plethora of therapeutic agents. The
high metabolic rate of the gut microbiome is due to the
many enzymes that catalyze reactions in the metabolism of
drugs. This high enzymatic activity of the intestinal microflora
is linked to the presence of P450 in the main bacterial
strains from the human fecal microbiota. The fact that many
intestinal bacterial strains have CYP enzymes (P450), arises
the question that if living probiotics express P450 activity it
could possibly influence the metabolism of drugs and their
bioavailability? (226).
In addition, if the intestinal barrier is disrupted (226–228), this
metabolism is affected. Undoubtedly, the role of probiotics is to
restore deficiencies and imbalance in the intestinal microbiome
and to establish a protective effect. Albeit that, the high enzymatic
activity of the intestinal microbiota as well as the action of
probiotics on the intestinal microbiome remain to be clarified.
It is obvious that future trials should focus on clarifying
the multifactorial association of the role of the cytochromes
CYP (P450) in the various disease states, environmental
toxic effects or chemical exposures and nutritional status.
It also worth to mention once more that the effectiveness
of a probiotics is strictly dependent on the strain and the
dose received.
Probiotics have a beneficial impact on the immune system
by stimulating non-specific immune response, improving several
disease states and alleviating allergies (Figure 2).
As it is well known, pathogens induce a pro-inflammatory
response in epithelial cells by activating transcription factor
activating transcription Nuclear Factor-κB (NF-kB) which keeps
a crucial role in immunity, inflammation, and cell proliferation.
There is evidence that probiotic strains have an effect on epithelial
immune activation by blocking this factor (229).
Administration of probiotics improves the immune system
in multiple ways; stimulated production of natural antibodies
IgM and IgG levels systemically, increased IgA antibodies locally
and systemically as well as interferon (230) and increased
phagocytosis ability which modulate cytokines presence (231). In
this spirit, probiotics have shown immunostimulatory effects that
may be associated to the initial inflammation following human
macrophages response (231).
It is emphasized that early intestinal colonization with
probiotic microorganisms such as Lactobacilli and Bifidobacteria
offers subsequent protection from many different types of
diseases. In addition, the beneficial probiotic microflora
dominated by Bifidobacteria and Lactobacilli could modify the
gut microbiota by reducing the risk of cancer following their
capacity to decrease β-glucoronidase and carcinogen levels (37).
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Stavropoulou and Bezirtzoglou Probiotics in Medicine
FIGURE 2 | Clinical use of probiotics in different disease states.
Moreover, probiotics are able to produce antimicrobial
substances,bacteriocins and lower the pH in order to inhibit
pathogens (232), compete for nutrients with pathogens and
finally enhance the intestinal barrier function (1,224).
The integrity of the intestinal barrier is a hallmark of a
healthy intestinal ecosystem (233). As discussed many factors are
contributing to this issue.
A variety of in vitro and animal studies implied the
significance of the human microbiota and the improvement of
the mucosal barrier function by probiotic treatment (3,234).
In spite of the aforementioned, there are difficulties to
extrapolate results of these studies to human populations.
Multiple clinical trials have been conducted so as to evaluate
the prophylactic and therapeutic effect of probiotics in different
diseases and states, especially in infections after the failure of
multiple courses of antibiotics.
At this point, we underpin that it is catalytic that more clinical
studies should be undertaken in a large sample of diseased
populations in order to evaluate the probiotics therapeutic
potential. Selection criteria, efficacy and safety issues of probiotics
should be considered as well as the fact that the probiotic ability
seems to be strain-dependent.
In this review, we tried to summarize current knowledge
on probiotics’ application and therapeutic potential in different
disease states and despite their possible benefits, the lack of
sufficient evidence for their efficacy and safety profile makes the
probiotic use a long-lasting debate.
AUTHOR CONTRIBUTIONS
ES focuses on all clinical aspects. All authors contributed to the
article and approved the submitted version.
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