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Characteristics of Listeria monocytogenes
... L. monocytogenes kasvaa 0-45 °C lämpötiloissa, kasvuympäristön ravinteista riippuen vaihtelevalla tehokkuudella (Junttila ym. 1988, Lou & Yousef 1999. L. monocytogeneksen on havaittu kasvavan myös tätä alhaisemmissa lämpötiloissa, kuten -0,1 °C --0,4 °C lämpötiloissa maidossa ja kanaliemessä (Walker ym. ...
... 1990). Alhaisin raportoitu kasvulämpötila on ollut -1,5 °C:ssa, vakuumipakatussa paahtopaistissa (Hudson ym., 1994) Yleensä yli 50 ºC lämpötilat tuhoavat L. monocytogeneksen (Lou & Yousef, 1999). Pastoröintiprosessi 71,7 ºC 15 sekunnin ajan on useimpien tutkimusten mukaan riittävä tuhoamaan maidossa olevat L. monocytogenes -bakteerit. ...
... Kasvuläpötila vaikuttaa L. monocytogeneksen lämmönkestävyyteen. Korkeassa lämpötilassa kasvaneet bakteerit kestävät lämpöä paremmin kuin matalammissa lämpötiloissa kasvaneet (Knabel ym., 1990;Farber & Pagotto, 1992;Lou & Yousef, 1999). L. monocytogenes -bakteerien kasvatus korkeassa lämpötilassa (43 °C) paransi lämpökestävyyttä enemmän kuin lämpösokki samassa lämpötilassa (43 °C) (Knabel ym., 1990). ...
... Listeriosis is a foodborne illness caused by Listeria monocytogenes. Listeriosis is a sporadic disease but has the highest fatality rate of 20-30% and hospitalization requirements of approximately 90% of foodborne illnesses (Lou & Yousef, 1999;Murphy & Meullenet, 2006). This bacterium causes two types of illness manifestations. ...
... This bacterium causes two types of illness manifestations. One is non-invasive, which is commonly called listerial gastroenteritis, where symptoms range from nothing to fever, vomiting, and diarrhea in healthy adults (Lou & Yousef, 1999). Invasive listeriosis, the second and most serious form of the disease, affects infants, pregnant women including their fetuses, immunocompromised individuals, such as AIDS and cancer patients, children, and the elderly (Lou & Yousef, 1999;Murphy & Meullenet, 2006). ...
... One is non-invasive, which is commonly called listerial gastroenteritis, where symptoms range from nothing to fever, vomiting, and diarrhea in healthy adults (Lou & Yousef, 1999). Invasive listeriosis, the second and most serious form of the disease, affects infants, pregnant women including their fetuses, immunocompromised individuals, such as AIDS and cancer patients, children, and the elderly (Lou & Yousef, 1999;Murphy & Meullenet, 2006). ...
There is great interest in the development of antimicrobial peptides as a potentially novel class of antimicrobial agents. In this study we evaluated the mode of action of new peptides (Gly-Val-His, Trp-His-Arg, Trp-His-Phe, Pro-Pro-Ser-Ser, Ala-Ala-Ala-Leu, Ala-Ala-Gly-Gly-Val, Ala-Ala-Val-Lys-Met, Ala-Ser-Ser-Ser), previously characterized, from barbel protein hydrolysates against Listeria monocytogenes via a membrane damage mechanism. The minimum inhibitory concentrations (MIC) of these peptides toward six strains and their hemolytic activity toward bovine erythrocytes were determined. Prediction of peptide secondary structure indicated that these peptides should have random coil structures and high content of hydrophobic amino acids. In addition, results of the determination of extracellular potassium, which is considered a good marker of membrane permeability, revealed that treatment with pure barbel peptides could cause morphological changes of L. monocytogenes and destruction of the cell integrity via irreversible membrane damage. The results could provide information for investigating the antibacterial model of antibacterial peptides derived from fish protein hydrolysates.
... Listeria monocytogenes can increase to high numbers in cured or noncured RTE meats during refrigerated storage due to its ability to survive and grow under low temperatures (Lou and Yousef 1999 surveillance and monitoring activities by FDA and USDA indicated that as much as 5% of certain RTE foods such as prepared deli-style salads and sliced luncheon meats contained L. monocytogenes (Hitchins 1996;Levine and others 2001). In 2005, the Foodborne Illness Active Surveillance Network (FoodNet) recorded a total of 16,614 laboratory-confirmed cases for pathogens, and of these, Listeria was responsible for 135 cases with an overall incidence level of 0.30 per 100,000 population (CDC 2006). ...
... If the a w in a product is lower than the minimum necessary for growth of L. monocytogenes, growth of the organism will be prevented or minimized provided the a w of the product does not increase during the shelf life or use of the product. Lou and Yousef (1999) studied the effect of different a w levels on the survival and/or growth of L. monocytogenes. They found the minimum a w was approximately 0.92 and 0.94, respectively, for growth of a variety of L. monocytogenes strains at 10 and 4°C when NaNO 2 was used. ...
... Sodium nitrite exerts some inhibitory effects against L. monocytogenes, although it does not consistently prevent growth at the concentrations remaining in many cooked meat products. This anti-listerial effect is enhanced at pH levels as <6.0 (Lou and Yousef 1999). In a study conducted by Shahamat and others (1980) on the efficacy of NaNO 2 for the control of L. monocytogenes, they determined that its activity was dependent on interactions with temperature, pH, and NaCl content. ...
... are known to survive and grow in aqueous environments such as canals, ditches, rivers, and lakes, and can adapt to an ever-changing environment. The organism is psychrophilic but grows best at 37 °C with an optimum water activity of ≥ 0.97 and can grow at a pH as low as 4.4 [16]. These stress responses allow Listeria to survive and multiply in the adverse environmental conditions often present in food production facilities [17,18]. ...
... are known to survive and grow in aqueous environments such as canals, ditches, rivers, and lakes, and can adapt to an ever-changing environment. The organism is psychrophilic but grows best at 37 • C with an optimum water activity of ≥ 0.97 and can grow at a pH as low as 4.4 [16]. These stress responses allow Listeria to survive and multiply in the adverse environmental conditions often present in food production facilities [17,18]. ...
Listeria monocytogenes, an intra-cellular, Gram-positive, pathogenic bacterium, is one of the leading agents of foodborne illnesses. The morbidity of human listeriosis is low, but it has a high mortality rate of approximately 20% to 30%. L. monocytogenes is a psychotropic organism, making it a significant threat to ready-to-eat (RTE) meat product food safety. Listeria contamination is associated with the food processing environment or post-cooking cross-contamination events. The potential use of antimicrobials in packaging can reduce foodborne disease risk and spoilage. Novel antimicrobials can be advantageous for limiting Listeria and improving the shelf life of RTE meat. This review will discuss the Listeria occurrence in RTE meat products and potential natural antimicrobial additives for controlling Listeria.
... Freezing was convenient for milk samples contaminated with L. monocytogenes. According to the bibliographic review performed by Lou and Yousef [1999], the bacteria may survive to temperatures below 0°C, depending on the strain, temperature, and medium. In particular, the milk matrix seems to provide a good protection against freezing [Lou and Yousef 1999]. ...
... According to the bibliographic review performed by Lou and Yousef [1999], the bacteria may survive to temperatures below 0°C, depending on the strain, temperature, and medium. In particular, the milk matrix seems to provide a good protection against freezing [Lou and Yousef 1999]. It can be noted that potential stress caused by freezing did not prevent the growth of L. monocytogenes and its recovery on selective agar. ...
... Addition of antimicrobial agents or preservatives to meat products, including sorbates, benzoates, and lactates, or curing agents such as sodium nitrite or salt, as well as treatment of products with acidifying agents like acetic and lactic acid, all constitute methods of chemical preservation. An example of biological preservation, or biopreservation, is fermentation where lactic acid bacteria may be used to inhibit the growth of spoilage and pathogenic microorganisms by the production of inhibitory metabolites by the lactic acid bacteria (297). Details of these processing and preservation methods are excellently reviewed by Claus et al. (298), van Laack (299) and Pearson and Gillett (300). ...
... Smoke is composed of many different compounds including alcohol, carbonyls, hydrocarbons and gases; however, the antimicrobial properties of smoke are due to phenols and acids present in the smoke, as well as the heat that is associated with wood smoking (300). Foodborne pathogens, including pathogenic E. coli and S. aureus are reportedly inactivated by commercially available liquid smoke products used in processed meats (297). ...
In general, the muscle tissues of healthy animals and birds, before slaughter, can be considered sterile. Exceptions to this generalization are the lymph nodes and some organs that may carry limited microbial contamination. In contrast, surfaces of the animal exposed to the environment such as hide, pelt, feathers, fleece, the mouth and the gastrointestinal tract may be heavily contaminated (6-8). These parts of the animal are the major sources of meat and poultry carcass contamination. The extent of contamination transfer from the above sources to the carcass is greatly dependent on the conditions under which animals are reared, slaughtered and processed (4,6-8). Hygienic practices, sanitation procedures, product handling and processing procedures, and conditions of storage and distribution are the most important factors that determine the microbiological quality of the final meat and poultry products. Consequently, variations in facilities, raising methods and practices of slaughtering and processing operations may lead to significant differences in the type and extent of meat contamination (4). Sources of contamination during processing, and the factors affecting the type and extent of contamination are discussed in the following sections.
... Addition of antimicrobial agents or preservatives to meat products, including sorbates, benzoates, and lactates, or curing agents such as sodium nitrite or salt, as well as treatment of products with acidifying agents like acetic and lactic acid, all constitute methods of chemical preservation. An example of biological preservation, or biopreservation, is fermentation where lactic acid bacteria may be used to inhibit the growth of spoilage and pathogenic microorganisms by the production of inhibitory metabolites by the lactic acid bacteria (297). Details of these processing and preservation methods are excellently reviewed by Claus et al. (298), van Laack (299) and Pearson and Gillett (300). ...
... Smoke is composed of many different compounds including alcohol, carbonyls, hydrocarbons and gases; however, the antimicrobial properties of smoke are due to phenols and acids present in the smoke, as well as the heat that is associated with wood smoking (300). Foodborne pathogens, including pathogenic E. coli and S. aureus are reportedly inactivated by commercially available liquid smoke products used in processed meats (297). ...
... L. monocytogenes can grow at wide pH range, pH 4.3-9.6. The minimum a w is as low as 0.90, but it can survive for extended periods even at lower a w values (Lou and Yousef 1999). L. monocytogenes has shown to grow at up to 12% NaCl (w/v) (Lou and Yousef 1999), thus limitation of the growth in foods by salt is unrealistic. ...
... The minimum a w is as low as 0.90, but it can survive for extended periods even at lower a w values (Lou and Yousef 1999). L. monocytogenes has shown to grow at up to 12% NaCl (w/v) (Lou and Yousef 1999), thus limitation of the growth in foods by salt is unrealistic. Even though the optimal growth temperature of L. monocytogenes is between 30 and 37 °C, it is able to grow at refrigeration temperatures and has shown to survive even freezing (Seeliger andJones 1986, Junttila et al. 1988). ...
R3-Nordic, the Nordic Association for Contamination Control, is a non-profit, independent association for the promotion of new technologies in contamination control in the Nordic countries. The venue of the annual symposium is Turku Polytechnic in the BioTurku region. The aim of the annual R3-Nordic Symposium is to provide knowledge of contamination control and clean room technology dealing with topics in the pharmaceutical, food and microelectronic industries. The topics at the 34th R3-Nordic Contamination Control Symposium are contamination control, clean room technology and management, regulations and standards in clean rooms, clean room clothing, isolation applications, R3 technology and air handling, environmental monitoring in production, process design, production hygiene, cleanability, cleaning and disinfection, risk assessment, risk management in packaging material production, quality systems, contamination control, occupational safety as well as production of pharmaceuticals, biopharmaceuticals, biomedicines and vaccines. We wish that this event will be fruitful in giving background information and new ideas to all participating in the symposium and people reading the proceedings.
... Listeria monocytogenes is an invasive foodborne pathogen that can cause serious disease in immuno-compromised individuals and pregnant women (Farber & Peterkin, 1991). It is common in many natural and manmade environments and can grow at refrigerated temperatures (Fenlon, 1999;Lou & Yousef, 1999). Although L. monocytogenes rarely causes diseases in the majority of the population, there is a zero-tolerance ruling issued by the U.S. Food and Drug Administration (1999) in ready-to-eat foods (including dairy products) because of high mortality rates. ...
... High prevalence of L. monocytogenes in food processing environments and in ready-to-eat food (Arimi et al., 1997;Autio et al., 1999) that has undergone pasteurisation, indicates that the process environment represents a significant source of L. monocytogenes in the finished products. The ability of L. monocytogenes to adhere to various food contact surfaces (Blackman & Frank, 1996;Hood & Zottola, 1997;Smoot & Pierson, 1998) and unusual growth and survival properties of the bacterium have supported these findings (Lou & Yousef, 1999). Other investigations, however, suggest that raw food material is the most likely source for L. monocytogenes (Eklund et al., 1995;Giovannacci et al., 1999). ...
The research work for the third Nordic dairy hygiene project P00027 DairyNET - Hygiene control in dairy environment, which has been funded by the Nordic Innovation Centre (formerly the Nordic Industrial Fund), has focused on hygiene and quality issues relating to raw milk, process surfaces, process waters, air and final products. The work was carried out in the Nordic dairies Aria Foods, Milko, Nordurmjolk, Norrmejerier, Skåne mejerier, TINE and Valio Ltd together with the research organisations BioCentrum-DTU, the Danish Technological Institute (DTI), the Icelandic Fisheries Laboratories (IFL), the Royal Institute of Technology (KTH), MATFORSK, SIK, the University of Akureyri and VTT Biotechnology as well as the following suppliers of chemicals, reagents and equipment: Finnsonic Oy, JohnsonDiversey, Lagafors Fabriks AB, Mjöll, TetraPak Nordic Processing and Orion Diagnostica Oy from May 2001 to October 2004. Decent Gun Wirtanen, VTT Biotechnology, co-ordinated the project. Mr. Oddur Gunnarsson was the senior advisor at the Nordic Innovation Centre for this project. The various studies were reported in the Nordic co-operation project DairyNET in order to achieve major synergy benefits through openminded discussions at the project meetings. New procedures in hygiene based on the project findings have been implemented in processing at the dairies.
... Salt content of fresh fish was low, as expected. Listeria can grow in nutrient broth with up to 10% of NaCl added (Lou and Yousef, 1999). It has been reported that LM grown in Brain Heart Infusion broth containing 6.5% NaCl, inoculated at 10 6 CFU/mL, showed a 3-log increase in 26 days at 4°C (Hudson, 1992). ...
... Evaluation of the impact of CPC on LM in seafood was accomplished using a nonpathogenic indicator such as LI. LI has been shown to have similar or higher growth and resistance profiles as LM (Lou and Yousef, 1999), has been cited as a suitable indicator organism for LM (Karaibrahimoglu et al., 2004), and has been used in numerous food studies. LI was shown to be a substitute for LM in thermal inactivation studies with skim milk (Fairchild and Foegeding, 1993) and for Camembert cheese processing (Liu et al., 2004). ...
Cetylpyridinium chloride (CPC) was evaluated as an antimicrobial against Listeria monocytogenes (LM) and Listeria innocua (LI) on fish. LI and LM showed the same reduction profile and the same minimum inhibitory and bactericidal concentrations. When CPC was applied to a diced fish matrix, reductions of 3.17–3.26 and 3.07–3.19 log were determined for LI and LM, respectively. Antimicrobial activity of CPC against LI resulted in initial reductions of 2.8–3.1 log in fresh fish fillets, 0.9–1.1 log in smoked fish fillets, and 3.2–3.4 log on fish skin. Effectiveness of CPC against total plate counts on fish skin showed reductions of 2.4–2.9 log.
... Faleiro et al. [23] studied the growth of L. monocytogenes in various broths and found that the bacteria was capable of growing in nutrient broth up to 10% added salt and in tryptose soy broth containing 25.5% (w/v) salt for up to 4 days. In food, L. monocytogenes is capable of growing in cabbage juice containing 5% salt [24], survival was detected in a 30% brine solution stored for > 60 days and in beef immersed in a 22% salt solution stored for 100 days [25]. Lowering a w of the growth media by the addition of salt creates an unfavourable environment for L. monocytogenes, which leads to reduced growth rates, extended lag phases and overall population decline [26]. ...
... Lowering a w of the growth media by the addition of salt creates an unfavourable environment for L. monocytogenes, which leads to reduced growth rates, extended lag phases and overall population decline [26]. Growth of L. monocytogenes has been observed at a w of 0.90 in TSB with added salt, and survival has been reported at an a w of 0.83 [25]. ...
Salt has been used in food preparation since pre-history and is still routinely added in modern food manufacturing processes. Salt may be added at the table or during cooking; however a large amount of dietary salt originates from processed foods (∼60-70% of adult daily dietary salt). Excess salt intake is strongly linked to increases in blood pressure (hypertension) and subsequently pre-disposes individuals to the onset of cardiovascular disease (CVD), a leading cause of death in developed countries. Excess dietary salt intake has also been linked to the development of kidney disease, aggravation of asthma conditions and to the onset of osteoporosis. Results from large numbers of human studies have led to worldwide initiatives being put in place in order to reduce current levels of salt consumption. Hence there is an urgent need to reduce excess dietary salt intake from processed foods in particular. Current daily consumption figures can be as high as ∼10-12g NaCl per day while an intake of 4g salt per day is sufficient. Therefore a target reduction to an intake of 6g per day is the goal for a number of public health agencies worldwide. An incremental reduction in salt content in foods appears to be the best strategy to reduce population blood pressure values. However any reduction in salt content in processed foods must not impact on product safety or sensory quality. In this review various public health aspects of salt intake are considered. Additionally, the technological implications of salt reduction in foods are discussed and the possibilities for replacement of salt by addition of salt replacers, herbs, spices and other food ingredients to maintain product quality are highlighted.
... Soil water content for each sample was measured according to the method provided by Conklin (2005) and Yousef (1999). 50 g of soil sample was weighted as wet weight. ...
... generally very slow as reported by Yousef and Lou. [50] Bacterium show optimum growth, multiplication and survival at 30-37°C and can grow up to 45°C optimum temperature is 37°C but can survive at a wide range of temperature. [51,52] Carpentier and Cerf [53] stated that L. monocytogenes is psychotropic and can grow under narrow range of temperature without proliferation. ...
isteria monocytogenes, Gram positive bacteria, rod-shaped, intracellular, opportunistic, invasive food borne bacterium, which is ubiquitous in nature. Soil, vegetation, sewage, water, and fecal materials are its primary source through which it reaches to our food system. It is one of the leading food borne bacteria which is pathogenic, causing Listeriosis in immunodeficient children, adult, pregnant women, central nervous system infection, bacteremia, and other clinical manifestation. Bacterium has arsenal of virulence factors Listeriolysin, phospholipases, internalins and Act A protein which help to enter, invade and infect the host cell, escape from autophagy and promote cell to cell spread. It can withstand diverse environmental parameters, that is, low temperatures, pH, osmotic and oxidative stress. Bacterium is deadly to humans and is food borne, causing economic losses and is a threat to food industry. Present review gives an overview of bacterial characteristics, etiology, isolation, distribution and pathogenicity of L. monocytogenes.Asian Pac. J. Health Sci., (2022);
... Following the contagion, people in the risk group, which may be listed as, pregnant women, newborns, old and immune deficient people are frequently affected by listeriosis (Slutsker and Schuchat, 1999). In severe infections, septicemia, meningitis and premature stillbirths are seen in humans whereas meningoencephalitis, abortus and mastitis present in domesticated animals (Farber et al., 1991 (Lou and Yousef, 1999). On the other hand, L. innocua is rarely associated with a disease yet commonly found during identification. ...
... withstand thermal treatment of 72.2°C for 16.4 s in an HTST pasteurizer. While discussing the adequacy of pasteurization, Lou and Yousef (1999) mentioned that "pasteurization is a safe process, which reduces the number of L. monocytogenes occurring in raw milk to levels that do not pose an appreciable risk to human health." They also noted that "although minimum HTST milk pasteurization is considered a safe process, most raw milk processing facilities have wisely adopted pasteurization temperatures well above the minimum legal limit." ...
In our previous study, we observed the sporadic presence of potentially heat-injured cells of Listeria innocua in ice cream mix following a selective enrichment protocol. Although injured cells have not yet been reported to cause any disease outbreaks, it is important to understand their presence in heat-treated food matrices. In this study, we propose a possible protective role of air pockets that may help explain the sporadic presence of potentially heat-injured cells following heat treatment. Challenge studies were conducted by inoculating ice cream mix samples (42% total solids, 16.3% fat, 22.2% total sugar, and 3.4% protein) with Listeria innocua (an established surrogate) at a mean spiking level of 4.0 log cfu/g. The inoculated samples were heat-treated at 69°C for 30 min and potentially heat-injured cells were detected using buffered Listeria enrichment broth, followed by plating on modified Oxford and Rapid'LMono agars. Scanning electron microscopy and atomic force microscopy were conducted on the air-dried, spiked ice cream mix samples, before and after the thermal treatment stages. Although direct plating did not reveal any intact cells in the heat-treated ice cream mix, a more sensitive enrichment protocol was able to identify cells that were potentially heat-injured. The scanning electron micrographs showed air pockets of different sizes in the ice cream mix samples. The spiked mix samples before heat treatment showed some Listeria cells unevenly distributed in the mix matrix and some entrapped within the larger air pockets. After heat treatment, scanning electron and atomic force micrographs showed cells entrapped only within the larger air pockets. The mix matrix, however, did not show any Listeria cells. Confirmation of Listeria at all stages of analysis was done using MALDI-TOF. These observations suggest that the Listeria cells could be entrapped within the larger air pockets and thus may undergo inadequate thermal effect. This could have resulted in their detection as potentially heat-injured cells, as evident under the conditions of the experiment. These results are preliminary observations and further studies are necessary to draw conclusions and understand the true implications of these findings.
... Holsinger et al. (1992) reported that, although the guidelines for pasteurization time-temperature of ice cream mix adequately inactivated L. monocytogenes, it is important to take every precaution to inactivate the organism, as some major ingredients of ice cream, such as stabilizers, are associated with the increased thermal tolerance, possibly through entrapment of the organism in the 3-dimensional network formed with casein micelle, as reported by Glicksman (1983). While concluding the adequacy of pasteurization, Lou and Yousef (1999) also reported on the general use of pasteurization temperatures well above the minimum legal limit being practiced by many raw milk processors. Additionally, Besse (2002), in a review, mentioned that it was not feasible to eliminate all bacteria with thermal treatment, as heating led to a physiological stress within cells, leaving them injured. ...
Listeriosis is a life-threatening infection caused by foods contaminated with Listeria monocytogenes. Some of the major ice cream recalls in recent years reaffirm the ability of this food-borne pathogen to survive in diverse dairy processing environments and cause cross contamination. Inspection reports revealed certain lapses in implementing adequate hygienic practices for Listeria persistence in the processing environment, leading to cross contamination of ice cream. The higher levels of cross contamination of raw ice cream mix might result in random heat-injured cells when exposed to minimum heat treatment (69°C for 30 min). These heat-injured cells could later recover under abusive storage and handling conditions and pose a health risk. Evidence about the presence of injured cells in ice cream mix may thus prove useful to establish the overall Listeria risk, which was the aim of this study. Challenge studies were conducted to evaluate the dose-dependent presence of heat-injured cells of Listeria. Ice cream mix formulations of 4 different types (36, 40, 42, and 45% total solids) were inoculated at 2.0, 3.0, and 4.0 log cfu/g levels of Listeria innocua (an established surrogate). The dose levels were selected based on a likely cross contamination on the raw side from environmental Listeria, especially due to their resident nature and growth in harborage sites. The samples were exposed to minimum heat treatment (69°C for 30 min) and the survivors, including heat-injured cells, were enumerated using standard protocols. A binary logistic regression model was fitted for evaluating the severity of risk. The influence of total solids, water activity, and pH variability were also studied on Listeria survival. The enrichment protocol, using buffered Listeria enrichment broth, followed by plating on modified oxford agar and Rapid L'mono medium, revealed the random presence of heat-injured cells in buffered Listeria enrichment broth, only at the highest dose level of 4+ logs. Any potential risk from heat-injured cells was thus limited only to the highest levels of cross contamination, irrespective of the type of the mix. Significantly, none of the pasteurized ice cream mix samples supported the recovery of any heat-injured cells of Listeria during 72 h holding at 7°C, even at the highest dose level of 4+ logs, under the conditions of experimentation. The level of cross contamination (dose) emerged as a predictor of the potential presence of heat-injured cells of Listeria exposed to minimum pasteurization treatment.
... Besides its capacity to infect mammalian hosts, it can grow at low temperatures, thus being characterized as a psychotropic bacterium, and in a wide range of water activity values (water activity is the ratio of the vapor pressure of a solution or food to the vapor pressure of water)-minimum of 0.90-0.93 and optimum above 0.97 (Lou and Yousef 1999). According to Buchanan et al. (2017), L. monocytogenes is commonly found in agricultural, aquacultural and food processing environments, besides being transiently found in the human gastrointestinal tract in rates varying from 2 to 10% of the general population. ...
Listeria monocytogenes is a Gram-positive bacterium commonly associated with foodborne diseases. Due its ability to survive under adverse environmental conditions and to form biofilm, this bacterium is a major concern for the food industry, since it can compromise sanitation procedures and increase the risk of post-processing contamination. Little is known about the interaction between L. monocytogenes and Gram-negative bacteria on biofilm formation. Thus, in order to evaluate this interaction, Escherichia coli and L. monocytogenes were tested for their ability to form biofilms together or in monoculture. We also aimed to evaluate the ability of L. monocytogenes 1/2a and its isogenic mutant strain (ΔprfA ΔsigB) to form biofilm in the presence of E. coli. We assessed the importance of the virulence regulators, PrfA and σB, in this process since they are involved in many aspects of L. monocytogenes pathogenicity. Biofilm formation was assessed using stainless steel AISI 304 #4 slides immersed into brain heart infusion broth, reconstituted powder milk and E. coli preconditioned medium at 25 °C. Our results indicated that a higher amount of biofilm was formed by the wild type strain of L. monocytogenes than by its isogenic mutant, indicating that prfA and sigB are important for biofilm development, especially maturation under our experimental conditions. The presence of E. coli or its metabolites in preconditioned medium did not influence biofilm formation by L. monocytogenes. Our results confirm the possibility of concomitant biofilm formation by L. monocytogenes and E. coli, two bacteria of major significance in the food industry.
... For example, in the outbreak of listeriosis in the United States in September 2011, a total of 146 invasive illnesses, 30 deaths, and 1 miscarriage were recorded (Laksanalamai et al., 2012). The foodborne pathogen Listeria, the causative agent of listeriosis (Yousef and Lou, 1999), can grow at refrigeration temperatures and adapt to low pH and high salt concentration (Cole et al., 1990). As such, this pathogen can overcome various bacteriostatic measures, increasing the difficulty of anti-listeria treatments. ...
Nisin, an important bacteriocin from Lactococcus lactis subsp., is primarily active against various Gram-positive bacteria. Leucocin C, produced by Leuconostoc carnosum 4010, is a class IIa bacteriocin used to inhibit the growth of Listeria monocytogenes. Because two bacteriocins have different modes of action, the combined use of them could be a potential strategy for effective inhibition of foodborne pathogens. In this study, L. lactis N8-r-lecCI (N8 harboring lecCI gene) coexpressing nisin–leucocin C was constructed based on the food-grade carrier L. lactis N8. Production of both bacteriocins was stably maintained. Antimicrobial measurements showed that the recombinant strain is effectively against Listeria monocytogenes and Staphylococcus aureus and moderately against Salmonella enterica serovar Enteritidis and Escherichia coli because of its stronger antibacterial activity than the parental strain, this result first demonstrated that the co-expression of nisin and leucocin C results in highly efficient antimicrobial activity. The checkerboard assay showed that the antibacterial activity of L. lactis N8-r-lecCI supernatant was enhanced in the presence of low concentration of EDTA. Analysis of the scanning electron microscope image showed the biggest cellular morphology change in L. monocytogenes treated with a mixture of EDTA and L. lactis N8-r-lecCI supernatant. The practical effect was verified in pasteurized milk through time-kill assay. The L. lactis N8-r-lecCI strain expressing both nisin and leucocin C has a promising application prospect in pasteurized milk processing and preservation because of its strong antibacterial activity.
... Listeria monocytogenes is considerably a strong bacterial species, however, it may be controlled through various measures; lowering pH value to 4.4 and water activity to 0.92 could inhibit the bacteria ( Tienungoon, Ratkowsky, McMeekin, & Ross, 2000). Low temperatures reduce L. monocytogenes growth and by 0 8C, most cells are supposed to be inhibited ( Lou & Yousef, 1999; U.S. FDA/FSIS, 2003). The official reports on foodborne outbreaks from L. monocytogenes indicated that the food products contamination with this bacteria is a continuing significant challenge, which needs more efficient measures/agents for its control (CDC, Centers for Disease Control and Prevention, 2013). ...
The anti‐listerial activity of various plant extracts was investigated, qualitatively and quantitatively against Listeria monocytogenes strains. The extracts of Punica granatum peels (PPE) and Hibiscus sabdariffa calyxes (RCE) exhibited the most potent antibacterial activity. The application of PPE and RCE, as colorant, preservative, and antimicrobial agents, was conducted for the manufacturing of fish products (burger and surimi). The two extracts could effectively enhance the microbial, sensory, and shelf life attributes of prepared fish products. The combination of the extracts at their inhibitory concentrations lead to complete inhibition of inoculated L. monocytogenes cells, enhancing the sensory attributes of treated fish products and increasing panelists' preference.
Practical applications
Foodborne pathogens' transmission via fish products, for example, L. monocytogenes , is hazardous and must be overcome efficiently and safely. The substitution of synthetic and chemical food additives and preservatives with natural agents is a general request from all. Results of study supported the practical application of powerful anti‐listerial plant extracts, for example, pomegranate peels and rosella calyxes, for the control of L. monocytogenes , coloring and improving sensorial attributes of processed fish products, burger and surimi.
... Listeria monocytogenes is a foodborne pathogen and the causative agent of listeriosis (Lou & Yousef, 2000). L. monocytogenes is able to form biofilms (Pan, Breidt, & Kathariou, 2006), can grow at low temperatures and can adapt to highly acidic or saline conditions (Cole, Jones, & Holyoak, 1990). ...
In this study, factors relevant to nature-ripened Gouda cheese were evaluated for their potential to inhibit growth of Listeria monocytogenes. Factors included water activity, pH, undissociated acetic and lactic acid, diacetyl, free fatty acids, lactoferrin, nitrate, nitrite and nisin. In addition, the effect of temperature was evaluated. For each factor, the actual concentrations and values relevant to Gouda cheese were obtained and the inhibitory effect of these individual factors on growth of L. monocytogenes was assessed. This evaluation revealed that undissociated lactic acid is the most important factor for growth inhibition of L. monocytogenes in Gouda cheese and that, additionally, low water activity as present in the cheese rind and after prolonged ripening times can also cause full growth inhibition. Gouda cheeses have a typical total lactic acid content of 1.47% w/w. In a 2-week old Gouda cheese, with a pH value of 5.25 and a moisture content of 42% w/w, the concentration of undissociated lactic acid in the water phase is 10.9 mM. Growth of L. monocytogenes is not supported when the undissociated lactic acid concentration is >6.35 mM. Concentrations of undissociated lactic acid in the water phase of Gouda cheese will be higher than this value when the total lactic acid content is >0.86% w/w at a pH < 5.25 (relevant to young Gouda cheese), or >1.26% w/w at a pH < 5.50 for mature Gouda cheese (moisture content of 35% w/w). This study underlines the importance of undissociated lactic acid as growth inhibitor for L. monocytogenes in Gouda cheese.
... It is well known the ability of L. monocytogenes to grow at very low temperatures, however, 4 C has been described as a critical point in terms of growth (Adams & Moss, 1995;Chan & Wiedmann, 2008). At this temperature, a slight increase can be enough to promote the growth with, e.g., faster growth rates (International Commission on Microbiological Specifications for Foods, 1996;Yousef & Lou, 1999), explaining that different growth dynamics between Tg concentrations appear at 4 C but not at 8 or at 20 C. An increased vulnerability of L. monocytogenes at suboptimal temperatures has been described for small changes in pH (Seeliger & Jones, 1986), a w (ICMSF, 1996) or certain components present in food (Angelidis & Smith, 2003;Bayles, Annous, & Wilkinson, 1996;Sleator, Francis, O'Beirne, Gahan, & Hill, 2003). ...
Tagatose is a novel low-calorie sweetener which addition changes food product properties, e.g., aw, and formula, that may influence food-microbial growth dynamics in both liquid and solid products. The aim of this work was to study growth dynamics of Salmonella Typhimurium and Listeria monocytogenes in liquid and solid media enriched with tagatose (1.5, 4.5 and 7.5% (w/v)), at 4, 8 and 20 °C. More specifically, liquid media were chemically defined minimal medium, general medium and UHT skimmed milk; gelatine and a gelatine-dextran mixture were the gelling agents used, leading respectively a homogeneous and heterogeneous solid system. At regular intervals, cell concentration was determined and the Baranyi and Roberts (1994) model was fitted for growth parameter estimation. Results show a reduced and even no growth of S. Typhimurium with increasing tagatose concentrations, especially at low temperatures and when increasing media complexity. The behaviour of L. monocytogenes is not affected by tagatose, except in liquid at 4 °C, where tagatose facilitates the growth in general culture media. Varying responses of the studied bacteria to changes in media formulation should be considered for future product design.
... Listeria spp. are able to survive under extreme physicochemical conditions such as refrigeration temperatures, low pH values and high salt concentrations (Lou & Yousef, 1999), promoting their persistence in fermented foods and on food processing equipment. Enterococci with potent anti-listeria activity have been isolated from a range of fermented food products and have been characterized previously (Aymerich et al., 1996;Casaus et al., 1997). ...
In this study, a total of 100 fermented food products including dairy (Lben, Rayeb, Rigouta, and Jben) olive and vegetable products, harvested in Northwestern Tunisia, were investigated for the presence of Enterococcus spp. Our results showed high levels of contamination with Enterococcus spp., identified according to standard bacteriological, biochemical and phenotypic criteria. 143 isolates were recovered; Enterococcus faecium (46.15%) was the predominant species, followed by Enterococcus faecalis (27.27%), Enterococcus casseliflavus (12.58%), E. durans (8.39%) and E. mundtii (5.59%). None of the isolates showed acquired resistance againts clinically relevant drugs used for enterococcal infections treatment in human medicins, and no haemolytic activity was demonstrated. Furthermore, over 50% of the isolates within each species exhibited antilisterial bacteriocin production. Further data are needed to enhance understanding of bacteriocin production of enterococci in fermented food products as well as the potential risks to quality and safety, including possible transmission of antibiotic resistant organisms to human consumers.
... The type of surface, nutrient level and type of microorganisms infl uence biofi lm development and production of extracellular material (Ronner and Wong, 1993). Environmental fl ora in food processing facilities may interfere with or enhance attachment of L. monocytogenes to surfaces or its growth in biofi lms (Lou and Yousef, 1999). It has been reported that in a fl owing system, Pseudomonas fragi, a bacterium which strongly attaches and produces exopolysaccharride materials on surfaces enhanced attachment of L. monocytogenes, but P. fragi itself failed to attach to these surfaces in this fl owing system (Sasahara and Zottola, 1993). ...
Both spoilage and pathogenic bacteria that grow in biofilms are more resistant to both physical and chemical methods to which similar planktonic cells are sensitive. In order to improve the destruction of bacterial cells in biofilms a number of new methods have been examined. Power ultrasound refers to sonic waves in frequencies ranging from 20 to 100 kHz. Power ultrasound has been shown to be effective in the removal of Pseudomonas aeruginosa, Escherichia coli and Listeria monocytogenes biofilms. Gas plasma discharge, magnetic fields and pulsed electric field have also been shown to reduce the biofilms of Pseudomonas aeruginosa and Staphylococcus aureus.
... This versatile facultative anaerobic microorganism has the ability to adapt quickly to environmental changes, which in turn makes it difficult to control. Not only is L. monocytogenes able to grow at temperatures ranging from 0 to 45°C, it can survive in freezing temperatures (-18°C and below) (Yousef 1999) and tolerate acidic conditions and low water activity (Nolan et al. 1992, O'Driscoll et al. 1996. Listeria monocytogenes expresses four to six peritrichous flagella which are responsible for its motility at room temperature and below. ...
... L. monocytogenes, however, can also enter the product both during and after processing due to poor sanitation conditions or inadequate manufacturing practices (Jinneman et al. 1999). L. monocytogenes survives freezing well and the frozen storage causes a limited reduction in the viable population of L. monocytogenes (Lou and Yousef 1999). ...
Imported (Saba) and local (Tilapia nilotica and Nile perch) flitted fish (60 samples) were analyzed for aerobic colony count (ACC), total coliform count and for presence of Listeria monocytogenes to detect their quality. Imported flitted fish samples were lower in aerobic colony count, coliform count and also in Listeria monocytogenes incidence. Aerobic colony count (ACC) was 3.3±7.7x10 6 cfu/g in imported (Saba) filleted fish, 1.8±4.0x10 7 and1.8±5.0x10 7 cfu/g in local filleted Tilapia nilotica and Nile perch, respectively. Coliforms counts were 1.3±2.8x10 2 , 4.3±8.4x10 2 and 5.1±3.2x10 2 cfu/g in imported (Saba) filleted, local filleted Tilapia nilotica and Nile perch, respectively. The overall incidence of Listeria monocytogenes was 6.7% in imported flitted fish samples, 23.3% in local flitted fish samples (26.7% in flitted Tilapia nilotica samples and 20% in Nile perch samples), which was identified by conventional PCR reaction.
... Although listeriosis infections are rare, the case-fatality rate is very high (20e30%), especially for the elderly, the unborn child, infants, and immune-compromised individuals (Doorduyn et al., 2006). L. monocytogenes may be found in a broad range of foods from animal or plant origin, and the microorganism can grow at pH values ranging from pH 4.4 to 9.0, at NaCl concentrations up to 12%, and temperatures from À0.4 to 44 C (Lou & Yousef, 2000). Food-borne outbreaks of L. monocytogenes have been associated with many different categories of food products, including seafood, vegetables, meat products and dairy products (EFSA, 2011), like soft and acid-curd cheeses made from pasteurised milk (Gaulin, Ramsay, & Bekal, 2012;Koch et al., 2010). ...
This challenge study demonstrates that Listeria monocytogenes does not grow in Gouda cheese: during the first 8 weeks of ripening no growth was observed and between 8 and 52 weeks viable numbers declined significantly in a well-established Gouda microcheese system. Cheese milk was artificially contaminated just prior to addition of the starter culture. Three individual L. monocytogenes strains were used, including strains originating from cheese, a cheese plant environment and a reference strain. During curd formation, viable numbers of L. monocytogenes increased by 0.5 log cfu g(-1), resulting from entrapment in the curd. No growth was observed during the first 8 weeks of ripening. A significant decline in the viable numbers of L. monocytogenes was observed in Gouda cheese that was ripened for longer than 8 weeks. Two factors that could possibly control the fate of L. monocytogenes in Gouda cheese were lactic acid and water activity.
... In the last case, a decrease in cytoplasm pH of the cell caused by the internalization of the undissociated organic acid molecules throughout storage time could explain the inactivation of those microorganisms studied. Lou and Yousef [38] indicated that the antimicrobial action of organic acids is attributed to cytoplasm acidification. The antimicrobial compounds added into dipping treatments exerted a significant (p<0.05) ...
The effectiveness of Panax ginseng (PG) combined with potassium sorbate (PS) and/or malic (MA) and citric (CA) acids against Salmonella enterica ser. Saintpaul, Escherichia coli O157:H7 and native microflora on fresh-cut mangoes and oranges was evaluated. A combination of PG 3% (w/v), MA 1% (w/v), PS 0.05% (w/v) achieved to reduce by more than 2.5 and 1.0 logs CFU/g Salmonella Saintpaul and E. coli O157:H7 populations, respectively, on fresh-cut mangoes and oranges just after added. Significant reductions (p<0.05) by more than 4 and 2 log CFU/g of Salmonella and E. coli O157:H7 populations, respectively, during 21 days of storage at 5ºC in fresh-cut mango and orange were also achieved. The native microflora growth was delayed with this combination of antimicrobials; and microbiological shelf-life of fresh-cut mangoes and oranges was extended by more than 20 days. Sensorial attributes of fresh-cut mango were not affected by the addition of antimicrobials.
... This pathogen is able to survive in a wide range of temperature, pH and NaCl concentration. In refrigerated stored meat, this bacterium can reach hazardous level (Lou and Yousef, 1999). In recent years, consumers demand for safety and fresh refrigerated foods with extended shelf life has increased (Sallam, 2007a). ...
In this study, the microbiological quality and lipid oxidation of the grass carp (Ctenopharyngodon idella) fillets treated by dipping in sodium acetate (0, 1 and 3%), nisin (0, 0.1 and 0.2%) or their combination were evaluated during 16 days of refrigeration storage. Antilisterial effect of nisin was enhanced with the increased concentration of sodium acetate. With increasing the concentrations of sodium acetate, mesophilic counts were lower but regarding nisin, better results were obtained by applying 0.1% nisin. Greater inhibition of mesophile bacteria was observed when combination treatment was used. The number of lactobacillus was lower when higher concentrations of sodium acetate and nisin were used. Peroxide, TBA and total viable base nitrogen (TVB-N) values were lower in the samples treated with both nisin and sodium acetate and higher results were obtained in the combination treatments.
... Raw milk is a wellrecognized vehicle of L. monocytogenes, with contamination generally occurring at low levels (13,21,31); nevertheless, through milk the pathogen can be transferred to cheese and other dairy foods, where it may survive, with or without growth, during processing and storage (15,18,22,25). L. monocytogenes contamination of cheese may be due to the use of raw or inadequately heated milk or to postthermal contamination of milk or curd (29,44,51) because this pathogen is exceptionally able to form biofilm on milk processing equipment (26,58) and is quite resistant to cheese-related stresses (30,43). To date, there have been several deadly listeriosis outbreaks linked with milk and cheese, mainly with the consumption of fresh, soft, or moldripened cheeses (9,24,25,53). ...
Recent research has shown that mild milk thermization treatments routinely used in traditional Greek cheese production are efficient to inactivate Listeria monocytogenes and other pathogenic or undesirable bacteria, but they also inactivate a great part of the autochthonous antagonistic
microbiota of raw milk. Therefore, in this study, the antilisterial activity of raw or thermized (63°C, 30 s) milk in the presence or absence of Lactococcus lactis subsp. cremoris M104, a wild, novel, nisin A–producing (Nis-A+) raw milk isolate, was assessed. Bulk milk
samples were taken from a local cheese plant before or after thermization and were inoculated with a five-strain cocktail of L. monocytogenes (approximately 4 log CFU/ml) or with the cocktail, as above, plus the Nis-A+ strain (approximately 6 log CFU/ml) as a bioprotective culture.
Heat-sterilized (121°C, 5 min) raw milk inoculated with L. monocytogenes was used as a control treatment. All milk samples were incubated at 37°C for 6 h and then at 18°C for an additional 66 h. L. monocytogenes grew abundantly (>8 log CFU/ml) in heat-sterilized
milk, whereas its growth was completely inhibited in all raw milk samples. Conversely, in thermized milk, L. monocytogenes increased by 2 log CFU/ml in the absence of strain M104, whereas its growth was completely inhibited in the presence of strain M104. Furthermore, nisin activity
was detected only in milk samples inoculated with strain M104. Thus, postthermal supplementation of thermized bulk milk with bioprotective L. lactis subsp. cremoris cultures replaces the natural antilisterial activity of raw milk reduced by thermization.
... Lack of proliferation but rather inactivation of L. monocytogenes in brine was likely the result of the high salt and acidic conditions. The highest concentrations of NaCl at which growth of L. monocytogenes have been observed are 10e12% (Lou & Yousef, 2000;Swaminathan, Cabanes, Zhang, & Cossart, 2007). The absence of growth, but survival and inactivation of L. monocytogenes in brine, is consistent with previous studies (Durmaz, Aygun, & Ardic, 2009;Larson, Johnson, & Nelson, 1999). ...
The fate of 3 different Listeria monocytogenes strains (Scott A, 2F and 6E) was studied independently in brine and on factory-scale Gouda cheeses that had been submerged in brine that was artificially contaminated with these individual strains. Viable numbers of L. monocytogenes in the brine decreased during brining (0, 1, 2.9 and 8.9 d). L. monocytogenes was enumerated on the surface of Gouda cheese directly after brining and over 26 weeks of ripening at 12.5 °C. Transfer of L. monocytogenes from brine to cheese during brining was limited. L. monocytogenes was detected in the outer layer of Gouda cheese but not in the centre directly after brining or during ripening. Throughout the ripening period, the viable numbers of L. monocytogenes declined significantly. This study adds to the understanding of the fate of L. monocytogenes in brine and on Gouda cheese, and demonstrates that growth of L. monocytogenes on Gouda cheese is not supported following contamination during brining.
... Listeria monocytogenes is an important human food-borne pathogen which causes febrile gastroenteritis in healthy individuals (Piana et al., 2005) and life-threatening invasive infections in susceptible individuals (Mead et al., 2006), such as the young, the old, the pregnant and the immune-compromised, the so called "YOPI" (De Cesare et al., 2006). In Europe it has an incidence of 0.3 cases/year/100,000 population (European Food Safety Authority, 2006), this pathogen has the ability to growth over a wide range of pH values (4.3 -9.6) (Lou and Yousef, 1999) and can survive under salt concentrations as high as 10% NaCl (McClure et al., 1989). Due to the ubiquitous nature of this pathogen in the slaughterhouse and the meat packaging environments, it is not surprising that the incidence and behavior of this pathogen in meat products are receiving increasing attention. ...
This study evaluated the effect of combinations of nisin with salt (NaCl) to control Listeria monocytogenes on sheep natural sausage casings. Casings were inoculated with 3.0 x 10 5 cfu/g final inocula of L. monocytogenes, stored at 6°C in different solutions of nisin at 0, 100, 150 and 200 µg/g. Each combined with salt at 0, 4, 7 and 12% (w/v). Samples were taken at day 0, 10, 20, 35, 60 and 90 post-inoculation and the number of bacteria present was determined. The bactericidal effect of nisin against L. monocytogenes cells was evident where nisin was applied in combination with salts. In all treatments, nisin/salt mixtures induced a bacterial growth inhibitory effect greater than salt alone. These results indicate that nisin and salt synergistically and significantly inhibit the growth of L. monoctogenes in sheep natural casings. The use of nisin combined with salt as antibacterial agent will be appropriate for applications on natural sausage casing industries as natural preservatives to control foodborne pathogens. They can be used as growth inhibitors of L. monocytogenes, an important foodborne pathogens and spoiling bacterium. The main reason for their appropriateness is their natural origin, which consumers find comforting. These beneficial characteristics could increase casings safety and shelf life.
... On the contrary, melon juice stored at 20 and 35°C did not inhibit the growth of L. monocytogenes, S. Enteritidis and E. coli O157:H7, since those populations increased significantly after 24 h (Tables 5-7). The microbial growth in melon juice is a direct consequence of its initial pH (Table 1), which is higher than the minimum pH for growth reported for L. monocytogenes (4.4), S. Enteritidis (3.99) and E. coli O157:H7 (4.0-4.5) in food (D'Aoust, Maurer, & Bailey, 2001;Lou & Yousef, 1999;Meng, Doyle, Zhao, & Zhao, 2001). Growth of L. innocua, S. Enteritidis and E. coli in melon juice at pH 5.91 stored at 35°C was also observed by Raybaudi-Massilia et al. (2006). ...
Minimal inhibitory (MIC) and minimal bactericidal (MBC) concentrations of malic acid against Listeria monocytogenes, Salmonella Enteritidis and Escherichia coli O157:H7 inoculated in apple, pear and melon juices stored at 5, 20 and 35 °C were evaluated. MICs and MBCs against L. monocytogenes, S. Enteritidis and E. coli O157:H7 were significantly affected by storage temperature, juice characteristics and type of microorganism. Malic acid was more effective at 35 and 20 °C than at 5 °C in all studied fruit juices. E. coli O157:H7 was more resistant to malic acid than S. Enteritidis and L. monocytogenes. Apple, pear and melon juices without malic acid were inhibitory to E. coli O157:H7, S. Enteritidis and L. monocytogenes at 5 °C, whereas, MBCs of 1.5% (v/v) of malic acid in apple and pear juices, and 2% (v/v) in melon juice at 5 °C were needed to reduce E. coli O157:H7, those concentrations being higher than those required to reduce S. Enteritidis and L. monocytogenes in those fruit juices. In addition, concentrations of 2%, 2.5% and 2.5% (v/v) of malic acid added to apple, pear and melon juices, respectively, were required to inactivate the three pathogens by more than 5 log cycles after 24 h of storage at 5 °C. Transmission electron microscopy showed that malic acid produced damage in the cell cytoplasm of pathogens without apparent changes in the cell membrane.
... In otherwise optimal conditions strains of L.monocytogenes have been reported to multiply at pH values as low as 4.3 (Lou and Yousef, 1999;Farber and Peterkin, 2000). The ability of listerias to multiply in these Portugese cheeses during maturation, storage and distribution, would depend on the pH of the cheeses, and also on the concentration of organic acids and of salt, and on moisture content and temperature. ...
A survey was made in 1995–1996 for Listeria spp. in 63 soft cheeses, made from raw ewe's milk using traditional methods, in the Province of Beira Baixa (Portugal). Listeria spp. were isolated from 47 (75%) of the cheeses, L.monocytogenes was isolated from 29 (46%), and L.innocua but not L.monocytogenes from 18 (29%). Of 24 isolates of L.monocytogenes that were serotyped, 20 were serotype 4b, three were serotype 1/2b and one was serotype 1/2a. Phage typing of isolates of L.monocytogenes and L.innocua showed that in some cases a particular phage type was associated with cheese from a particular source. Twenty four strains of L.monocytogenes tested were able to grow at 30°C in culture medium adjusted with HCl to a pH in the range from 4.4 to 6.0 within 3 days; in the pH range 4.4–6.8 a representative strain grew most rapidly at pH 6.8. The pH range in the cheeses during maturation was between about 5.2–6.4. Whether L.monocytogenes could multiply in the cheeses would depend on factors such as concentration of organic acids and of salt, and storage temperature.
... L. monocytogenes is the causative agent of a wide range of pathologies, ranging from gastroenteritis to meningitis and abortion, with mortality rates of 20-30%, and has long been recognised as one of the most important food safety issues to address (Aureli et al. 2000;Lundén et al. 2004;Cossart and Toledo-Arana 2008). It is able to survive under severe physicochemical conditions such as refrigeration temperatures, low pH values and high salt concentrations (Lou and Yousef 1999), promoting persistence in foods and on food processing equipment. ...
Enterococcus faecium MMRA is an enterocin A producer isolated from ‘Rayeb’, a Tunisian fermented milk drink. In this work, safety aspects and
its behaviour in raw milk were investigated to assess its suitability as a protective adjunct culture. E. faecium MMRA showed interesting features such as the absence of several virulence traits, susceptibility to vancomycin and other
clinically relevant antibiotics, and lack of haemolytic activity. To evaluate its performance as an adjunct culture for Rayeb,
changes in the overall composition of control (non-inoculated) and experimental Rayeb (inoculated with 1%, v/v, E. faecium MMRA) were determined throughout duplicate fermentations of raw milk using microbiological, chemical, HPLC and headspace
GC-MS analyses. E. faecium MMRA could multiply in raw milk and produced enterocin A. Interestingly, a higher content of volatile compounds including
ethanol, diacetyl and 2-propanol was observed in the presence of this bacteriocin producer. Furthermore, this strain was capable
of inhibiting the growth of Listeria monocytogenes CECT 4032 in pasteurised milk, although total killing was not achieved. Further experiments confirmed the development of
resistant variants to enterocin A. On similar challenge assays, L. monocytogenes CECT 5672 growth was halted by the presence of the enterocin producer, but viability was only slightly reduced during cold
storage. According to our results, E. faecium MMRA meets the criteria for an autochthonous protective adjunct culture to enhance both the hygienic and the sensory attributes
of Rayeb.
... Numerous processing and preservation methods have been tested against L. monocytogenes [9], however little information is available about HHP and its ability to reduce pathogenic microorganisms [1,12]. S. aureus on the other hand has been reported to be the most pressure-resistant pathogen among the other pathogens tested under pressure [3,10]. ...
By the application of HHP; 5.50 and 5.70 log cycle reduction was obtained for S. aureus 485, in milk and cream of chicken soup samples, respectively. Storage of HHP treated milk samples for 24 h at 4 °C gave positive result for S. aureus 765 where no growth was observed for L. monocytogenes strains. Incubation of food samples for an additional 48 h at 37 °C showed growth of L. monocytogenes strains as S. aureus strains. When a bacteriocin-based biopreservative (BP 1 ) was combined with pressurization more than 8 log-cycle reduction in cell population of the resistant strains of S. aureus and L. monocytogenes was achieved in milk. Milk and cream of chicken soup samples were stored at 25 °C and milk samples showed no growth up to 30 day where as Gram-positive bacterial strains in cream of chicken showed growth after 3 days with a rapid increase in cell number thereafter.
... A typical bacterium that causes hygiene and safety problems in foodprocessing equipment is L. monocytogenes. It can become attached to diVerent surfaces and tolerate low temperatures (Mafu, Denis, Goulet, & Magny, 1990; Walker, Ascher, & Banks, 1990), anaerobic (Buchanan, Stahl, & Whiring, 1989) and other process conditions, e.g. a wide pH range (Lou & Yousef, 1999 ), and also persist in food-processing equipment (Lundén et al., 2003). This bacterium can also be found on hands or gloves used in food-handling (Autio et al., 1999; Destro, Leitao, & Farber, 1996). ...
The hygienic working practices of the maintenance personnel as well as the hygiene of the equipment in the food industry were investigated with questionnaires and microbial surveys. The protective clothing, washing of hands and tools as well as avoiding for-eign bodies left on the production lines should be targeted when the hygienic working practices are developed for maintenance per-sonnel. Based on the questionnaire to food processors, packaging machines, conveyers, dispensers, slicing and cooling machines were considered the most problematic pieces of equipment hygienically mainly because of poor hygienic design. In order to improve food safety, both the training of maintenance personnel in food hygiene and equipment design should be more emphasised.
Listeria monocytogenes is a ubiquitous foodborne pathogen that results in a high rate of mortality in sensitive and immunocompromised people. Contamination of food with L. monocytogenes is thought to occur during food-processing, most often as a result of the pathogen producing a biofilm that persists in the environment, and acting as the source for subsequent dispersal of cells onto food. A survey of seafood-processing plants in New Zealand identified the persistent strain 15G01, which has a high capacity to form biofilms. In this study, a transposon library of L. monocytogenes 15G01 was screened for mutants with altered biofilm formation, assessed by a crystal violet assay, to identify genes involved in biofilm formation. This screen identified 36 transposants that showed a significant change in biofilm formation compared to the wild-type. The insertion sites were in 27 genes, of which 20 led to decreased biofilm formation and seven to an increase. Two insertions were in intergenic regions. Annotation of the genes suggested that they are involved in diverse cellular processes, including stress response, autolysis, transporter systems and cell wall/membrane synthesis. Analysis of the biofilms produced by the transposants using scanning electron microscopy and fluorescence microscopy showed notable differences in the structure of the biofilms when compared with the wild-type. In particular, inactivation of uvrB and mltD produced coccoid-shaped cells and elongated cells in long chains, respectively, and the mgtB mutant produced a unique biofilm with a sandwich structure which was reversed to the wild-type level upon magnesium addition. The mltD transposant was successfully complemented with the wild-type gene, whereas the phenotypes were not or only partially restored for the remaining mutants.
Importance
The major source of contamination of food with Listeria monocytogenes is thought to be due to biofilm formation and/or persistence in food-processing plants. By establishing as a biofilm, cells become harder to eradicate due to their increased resistance to environmental threats. Understanding the genes involved in biofilm formation and their influence on biofilm structure will help identify new ways to eliminate harmful biofilms in food processing environments. To date multiple genes have been identified as involved in biofilm formation of L. monocytogenes , however, the exact mechanism remains unclear. This study has identified four genes associated with biofilm formation in a persistent strain. Extensive microscopic analysis illustrated the effect of the disruption of mgtB , clsA , uvrB and mltD and the influence of magnesium on the biofilm structure. This work strongly suggests an involvement in biofilm formation for the four genes and provides a basis for further studies to analyse gene regulation to assess the specific role of these biofilm-associated genes.
Background and Aims: The purpose of this study was to investigate the possibility of Listeria monocytogenes entering the VBNC state during the frozen storage and the expression of its pathogenic genes
Materials and Methods: Bacteria in 106 Colony counts of in mid log phase were inoculated into three Culture medium including Normal Saline (NS), BHI Broth and Fish Broth (FB) and kept at -18ºCfor 2 months and examined. Then, bacteria were evaluated on enriched medium BHI agar using culture methods (colony count) over times 4 and 8 hours, 2, 4, 8, 20, 30 and 60 days after the freezing shock using the method of RT-PCR for investigating the expression of 16S rRNA, hly and inlA genes; they were evaluated before and after the freezing shock.
Results: This bacterium retained its ability to cultivate until the end of the shock, but reduced its number. Freezing stopped the expression of genes of hly and inlA, as these genes were not expressed in a rich culture medium either. By adding blood to the rich culture medium of this bacterium, only the hemolysin O pathogen gene was expressed.
Conclusion: Although freezing does not lead to the introduction of this bacterium into the VBNC state, it is effective as an adverse environmental factor for the bacteria in the expression of its pathogenic genes. Blood and its agents can act as an agent for the induction and clarification of the hly gene, and the expression of pathogenic bacterial genes are independent of each other.
Based on their extensive experience working within the food industry and supported by published reports and research work, the authors describe in sections titled with self-explanatory headings the key characteristics of Listeria monocytogenes that help to explain why it is an important foodborne pathogen and approaches to the monitoring and control of the organism in food production processes.
The reporting of L monocytogenes in food in Colombia is not a mandatory; however, foods considered high-risk are monitored, and the organism is only reported clinically as Gram-positive when it causes meningitis. L. monocytogenes is a foodborne, intracellular, pathogen which causes listeriosis, a disease lethal to humans and animals. Outbreaks of this disease worldwide can bring about human and economic losses. Only a few studies in Colombia have been able to identify and molecularly serotype isolates allowing only the theoretical distribution of serotypes by lineage. This review explains the characteristics of the pathogen, its importance in public health and in the food industry, and provides an overview of PFGE-CHEF; identifying the standard work protocol and the appropriate restriction enzymes to cut DNA. We found that the enzyme combination, Xbal-AscI, followed by ApaI offers the best results to differentiate isolates, by grouping them by lineages, and displaying intra-serotype variations. Additionally, we found that in several Latin American countries the results are analyzed using PulseNet; this ensures the comparison of PFGE patterns in equivalent conditions.
Listeria monocytogenes is an important food associated pathogen because of its relatively high heat resistance and ability to multiply
in refrigeration temperatures. Its thermotolerance can be increased when its cells are subjected to heat shock. One- to eight-fold increase
of D values of L. monocytogenes have been reported, depending on the heat shock duration, the temperature and the heating menstrum.
This acquisition of heat tolerance is related to the induction of the synthesis of heat shock proteins (HSPs).
The adaptive response of food pathogens has important consequences on the safety of thermally processed foods. It is believed that
this is responsible for the frequent occurrence of deviations (tails and shoulders) during heat treatments that are observed in the exponential
model of microbial inactivation. These deviations from log-linear kinetic especially encountered under mild heat treatments,
mean that prediction of food safety can no longer rely upon D and z values. Adaptive response to heat must be considered when quantifying
and modeling microbial inactivation during thermal processing in order to achieve microbiologically safe products without overly
conservative heat processes. Therefore a more mechanistic approach is needed for more accurate predictions of thermal inactivation.
Prerequisite to this model are thorough studies to understand how L. monocytogenes and other pathogens adapt their cellular physiology
to overcome heat and other stresses.
Pulsed light (PL) treatments have emerged as a non-thermal method for microbial decontamination on foods surfaces. The aim of this work was to evaluate the bactericidal effect of PL by identifying the spectral range with antimicrobial activity and its effect on the quality of fresh-cut mushrooms (Agaricus bisporus). The mechanism responsible for their action on bacterial cells was also studied using Transmission Electron Microscopy (TEM). Results show that the effectiveness of PL-treatment decreases when the UV (ultraviolet) spectral region is blocked (particularly UV-C). PL treatments of full wavelength spectrum (180–1100 nm) and a fluence of 12 J/cm2 caused 3 and 2 log reductions in the initial counts of inoculated Escherichia coli and Listeria innocua, respectively. TEM showed significant damage in cell cytoplasm and cytoplasmic membrane after treatments with full spectrum pulses and a total fluence of 12 J/cm2. In contrast, mushroom cells treated with 6 J/cm2 did not exhibit apparent changes in their cytoplasmic membrane. Full spectrum treatments had a more pronounced impact on color, texture and headspace gas composition than treatments without UV spectrum profile. This work contributes with new information regarding the effects of the spectral range of PL treatments that the whole UV–Vis range of the spectrum accounts for the lethal effect against microorganisms. On the other hand, it also provides increased knowledge regarding the antimicrobial action of this technology, showing that a photophysical effect exists, leading to changes in the bacterial cytoplasmic membrane and cell content.
In this study, antimicrobial activities of the four different extracts (in methanol, ethanol, n‐hexane and water) of some herbs including Allium vineale, Chaerophyllum macropodum, and Prangos ferulacea were investigated against Listeria monocytogenes serovars 1/2b, 4b, and 4ab. For many centuries, these herbs were used in food production in Turkey. While water extracts of all the plants did not show any antibacterial activity, the other extracts of these plants showed variable degrees of antibacterial activity against L. monocytogenes serovars tested. The extracts of Allium vineale showed higher antibacterial activity than the other plants. The methanol extracts of all the plants exhibited higher activity than the ethanol and n-hexane extracts. L. monocytogenes 4ab was the most sensitive serovar to extracts of these plants. The results indicated that the methanol and ethanol extracts of these plants displayed remarkable activity against L. monocytogenes serovars and therefore, they could be used as natural anti-Listeria monocytogenes additives in herby cheese.
Listeria monocytogenes is well recognized as a serious foodborne pathogen in humans. However, the performance of methods for detection and enumeration may be altered by large amounts of stressed cells within the L. monocytogenes population. Many results have been published which concern factors affecting the recovery of injured L. monocytogenes: they include temperature, atmosphere, pH, and the addition of various components to the media, including sugars, yeast extracts, egg yolk, salt, osmoprotectants, cations, reducing agents and antioxidant enzymes. Current analytical methods for L. monocytogenes have also been compared regarding their ability to recover stressed Listeria. Moreover, research has focused on the development of methods, including an improved resuscitation step. A review of these studies is presented in this paper.
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