Nan Li

University of Florida | UF

Background MDR Staphylococcus aureus infections, along with the severity of biofilm-associated infections, continue to threaten human health to a great extent. It necessitates the urgent development of novel antimicrobial and antibiofilm agents. Objectives To reveal the mechanism and target of cinacalcet as an antibacterial and antimicrobial agent...

Objective Antibiotics are one of the most widely used medications in today's neonatal intensive care units. Indiscriminate antibiotic usage persists in preterm newborns who are symptomatic due to factors linked to prematurity rather than being septic. Previous studies in older infants suggest that prior antibiotic administration is associated with...

Objective Assess presence, durability, and neutralization capacity of SARS-CoV-2-specific antibodies in breastfeeding infants’ stool, mother’s plasma and milk following maternal vaccination. Design Thirty-seven mothers and 25 infants were enrolled between December 2020 and November 2021 for this prospective observational study. All mothers were va...

Objective: Enteral feeding tubes are used in neonatal intensive care units (NICUs) to assess feeding tolerance by utilizing preprandial gastric residual aspiration. This study evaluates the effect of gastric residual aspiration on the preterm infant fecal microbiome and gastrointestinal inflammation. Study design: Fifty-one very low birth weight...

Infections caused by drug-resistant bacteria are a serious threat to public health worldwide, and the discovery of novel antibacterial compounds is urgently needed. Here, we screened an FDA-approved small-molecule library and found that crizotinib possesses good antimicrobial efficacy against Gram-positive bacteria. Crizotinib was found to increase...

In most bacteria, iron plays an important role in the survival of bacteria and the process of infection to the host. Streptococcus pneumoniae (S. pneumoniae) evolved three iron transporters (i.e., PiaABC, PiuABC, and PitABC) responsible for the transportation of three kinds of iron (i.e., ferrichrome, hemin, and ferric ion). Our previous study show...

In December 2020, efficacious COVID-19 vaccines were approved for use and since, millions have been immunized against SARS-CoV-2, the virus responsible for COVID-19. It is known that administration of the COVID-19 vaccine leads to increased SARS-CoV-2 specific antibodies in plasma and human milk. While this increase has been studied, the durability...

Iron is an essential element for bacterial virulence and infection of the host. The detailed hemin metabolism in Gram-positive bacteria has rarely been studied.

Background: In 2019, a deadly virus known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), responsible for coronavirus disease 2019 (COVID-19), emerged. In December 2020, two mRNA-based COVID-19 vaccines were approved for use in the United States, which provide immunity to those receiving the vaccine. Maternally derived antibodies a...

In 2019, a deadly virus known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), responsible for COVID-19, emerged. Two mRNA-based COVID-19 vaccines were approved for use in December 2020 in the US and have begun providing immunity to those receiving the vaccination. Certain vaccines given to pregnant and lactating mothers provide imm...

Antibiotic use in neonates can have detrimental effects on the developing gut microbiome, increasing the risk of morbidity. A majority of preterm neonates receive antibiotics after birth without clear evidence to guide this practice. Here microbiome, metabolomic, and immune marker results from the routine early antibiotic use in symptomatic preterm...

We enrolled 98 infants (gestational age <33 weeks) in a pilot randomized trial of antibiotics vs no antibiotics; 55 were randomized (lower maternal infectious risk; symptoms expected for gestation). Adverse events did not differ significantly between the randomization arms. This trial establishes a framework for a larger multicentered trial.

Within a randomized prospective pilot study of preterm infants born at less than 33 weeks’ gestation, weekly fecal samples from 19 infants were collected and metabolomic analysis was performed. The objective was to evaluate for differences in fecal metabolites in infants exposed to antibiotics vs. not exposed to antibiotics in the first 48 h after...

Capsular polysaccharide is a key factor underlying the virulence of Streptococcus pneumoniae in human diseases. Thus, a deep understanding of capsular polysaccharide synthesis is essential for uncovering the pathogenesis of S. pneumoniae infection. In this study, we show that protein SPD_1495 interacts with phosphorylated ComE to negatively regulat...

Objective: To determine the effect of gastric residual aspiration and evaluation on preterm very low birth weight infants' gastrointestinal function, intestinal inflammation, and gastrointestinal mucosal bleeding. Study design: This single-center, randomized trial compared omission of gastric residuals vs prefeed gastric residuals in 143 infants...

In most bacteria, iron plays a vital role in pathogenesis processes. To support survival and infection, Streptococcus pneumoniae has evolved three ABC transporters, PiaABC, PiuABC, and PitABC. Moreover, indirect evidence supports that operon 804 may be a novel ABC transporter in S. pneumoniae. We have recently described the identification of lipopr...

Importance Evaluating prefeed gastric residuals is considered routine care but has little supporting evidence. Objective To determine the effect of omitting prefeed gastric residual evaluation on nutritional outcomes in extremely preterm infants. Design, Setting, and Participants This single-center randomized clinical trial compared the omission...

The purpose of this prospective cross-sectional cohort pilot study is to explore the initial microbial community of gastric aspirate fluid as collected immediately after birth and its relationships with mode of delivery and preterm birth. Twenty-nine gastric aspirate samples collected immediately after birth from infants born between 24-40 weeks ge...

Human milk contains beneficial nutrients for newborn infants. However, the most recent findings are that live microbes are an important component of human milk. These microbes may play a role in providing beneficial components to promote healthy development in infants. Preterm infants that have a gestation age of less than 30 weeks are provided wit...

Zinc is an essential metal in bacteria. One important bacterial zinc transporter is AdcA, and most bacteria possess AdcA homologs that are single-domain small proteins owing to better efficiency of protein biogenesis. However, a double-domain AdcA with two zinc-binding sites is significantly overrepresented in Streptococcus species, many of which a...

Purpose Low levels of the long chain polyunsaturated fatty acid (LCPUFA) docosahexaenoic acid (DHA) have been implicated in retinopathy of prematurity (ROP). However, oral DHA suffers from poor palatability and is associated with increased bleeding in premature infants. We asked whether oral administration of the neutraceutical arginine-glutamine (...

The American Academy of Pediatrics recommends that extremely preterm infants receive mother’s own milk (MOM) when available or pasteurized donor breast milk (DBM) when MOM is unavailable. The goal of this study was to determine whether DBM could be inoculated with MOM from mothers of preterm infants to restore the live microbiota (RM). Culture depe...

The pathogenic Streptococcus pneumoniae (S. pneumoniae) has evolved a special mechanism such as pneumococcal iron acquisition ATP binding cassette (PiaABC)to take up siderophore-iron from its host. The cell-surface lipoprotein PiaA, a key component of PiaABC, is the primary receptor to bind ferrichrome (Fc). To study the structure-function relation...

Premature infants are exposed to various perinatal stresses, including hypotension, hypoxia, hyperoxia, hypothermia, feeding, anemia, and umbilical vessel catheterization. Hypoxia-associated small intestinal injury may occur in a variety of severe pathophysiologic conditions in pediatric patients such as perinatal asphyxia, shock, or other hypoxic-...

Unlabelled: Streptococcus pneumoniae is a Gram-positive pathogen that causes a variety of infection diseases in human. In this project, we determined the antibacterial activity of a Ru(II) complex X-03 against S. pneumoniae in vitro, by comparing its toxicity to host cells A549 and HBE. We performed two-dimensional gel electrophoresis (2-DE)-based...

Iron is an essential nutrient for the growth of most bacteria. To obtain iron, bacteria have developed specific iron-transport systems located on the membrane surface to uptake iron and iron complexes such as ferrichrome. Interference with the iron-acquisition systems should be therefore an efficient strategy to suppress bacterial growth and infect...

Streptococcus pyogenes is an important human bacterium with high pathogenicity. Heme is a major source of iron that plays a critical role in bacterial survival and virulence. In this study, heme-affinity chromatography, two-dimensional-electrophoresis and mass spectrometry were combined to identify putative heme-binding proteins and heme-regulatory...

Preterm birth is the second leading cause of death in children under the age of five years worldwide, but the etiology of many cases remains enigmatic. The dogma that the fetus resides in a sterile environment is being challenged by recent findings and the question has arisen whether microbes that colonize the fetus may be related to preterm birth....

Streptococcus pneumoniae is a Gram-positive pathogen responsible for pneumonia, otitis media, and meningitis. Manganese and zinc ions are essential for this bacterium, playing regulatory, structural, or catalytic roles as the critical cofactors in the bacterial proteins and metabolic enzymes. Lipoprotein PsaA has been found to mediate Mn(2+) and Zn...

Necrotizing enterocolitis (NEC) is an enigmatic disease that affects primarily premature infants. It often occurs suddenly and when it occurs, treatment attempts at treatment often fail and results in death. If the infant survives, there is a significant risk of long term sequelae including neurodevelopmental delays. The pathophysiology of NEC is p...

Background: Necrotizing enterocolitis (NEC) is a major cause of death and morbidity in very low birth weight infants. Objective: To identify biomarker(s) that would predict NEC using buccal swab samples utilizing a proteomic approach. Methods: Cumulative buccal swab samples derived from very low birth weight preterm infants (<32 weeks' gestati...

Lipoprotein FtsB is a component of the FtsABCD transporter that is responsible for ferrichrome binding and uptake in the Gram-positive pathogen Streptococcus pyogenes. In the present study, FtsB was cloned and purified from the bacteria and its Fch binding characteristics were investigated in detail by using various biophysical and biochemical meth...

Kinetics curve of Fch binding with W204 mutant. (TIF)

pH dependence of Fch binding with FtsB. (TIF)

Mass spectrum of purified FtsB (upper panel) and database searching report (lower panel). (TIF)

Late onset sepsis (LOS) is a major contributor to neonatal morbidity and mortality, especially in premature infants. Distortions in the establishment of normal gut microbiota, commensal microbes that colonize the digestive tract, might increase the risk of LOS via disruption of the mucosal barrier with resultant translocation of luminal contents. C...

Supplementation studies of glutamine, arginine, and docosahexaenoic acid (DHA) have established the safety of each of these nutrients in neonates. However, the potential for a more stable and soluble dipeptide, arginyl-glutamine (Arg-Gln) or DHA, a long-chain ω-3 fatty acid with anti-inflammatory properties, to exert benefits on hyperoxia-induced l...

Purpose: Late onset sepsis (LOS) is a major cause of morbidity and mortality in the neonate. Determination of the intestinal microbial colonization may indicate who is at risk for microbial translocation and LOS. Hypothesis: septic infants compared to control infants would differ in their microbial colonization patterns and secondarily that the use...

Background Necrotizing Enterocolitis (NEC) is a major cause of death and morbidity in very low birth weight (VLBW) infants. IL‐1ra is the competitive receptor antagonist for IL‐1 a cytokine that promotes inflammation and causes an increase in intestinal epithelial tight junction permeability. Hypothesis Buccal sample proteomic analysis will provid...

Our previous study showed that low dose flagellin (LDFL) promotes tolerance to pathogenic ligand flagellin (HDFL)‐induced IL‐8 production in Caco‐2 cells. HDFL at 500 ng/ml increased IL‐8 by 19 fold and pretreatment with LDFL at 10 ng/ml reduced HDFL‐induced IL‐8 by 52%. Using a signaling pathway microarray and systems biology analysis, the toll‐li...

Supplementation studies of glutamine, arginine, and docosahexaenoic acid (DHA) have established the safety of each of these nutrients in neonates; however, the potential for a more stable and soluble dipeptide, arginyl-glutamine (Arg-Gln) or DHA with anti-inflammatory properties, to exert benefits on hyperoxia-induced intestinal injury has not been...

Intestinal luminal microbiota likely contribute to the etiology of necrotizing enterocolitis (NEC), a common disease in preterm infants. Microbiota development, a cascade of initial colonization events leading to the establishment of a diverse commensal microbiota, can now be studied in preterm infants using powerful molecular tools. Starting with...

Lactobacillus johnsonii (Ljo) N6.2 has been shown to mitigate the development of type 1 diabetes when administered to diabetes-prone rats. The specific mechanisms underlying this observed response remain under investigation. The objective of this study was to assess the effect of Ljo N6.2 on mucosal inflammatory response using differentiated Caco-2...

Although it is known that resident gut flora contribute to immune system function and homeostasis, their role in the progression of the autoimmune disease type 1 diabetes (T1D) is poorly understood. Comparison of stool samples isolated from Bio-Breeding rats, a classic model of T1D, shows that distinct bacterial populations reside in spontaneous Bi...

Aims: Using a model of hyperoxia-induced brain injury, we evaluated the potential for Arg-Gln or DHA to counteract the impact of hyperoxia in the developing brain.Methods: 7-day old pups and their nursing dams were placed in 75% oxygen for five days. Pups were returned to room air on postnatal day 12 (P12) and supplemented by oral gavage twice dail...

Aims: ROP is the leading cause of blindness in children. The most abundant sphingolipid in retinal membranes, sphingomyelin (S), is converted to ceramide (C) by acid sphingomyelinase; C/S ratio indicates inflammation and retinal injury. We compared the effects of Arg-Gln dipeptide, alone or with DHA on NV, VR and C/S ratio in a model of ROP.

An intestinal permeability defect precedes type 1 diabetes mellitus and may be a permissive factor in its pathogenesis. Butyrate strengthens the intestinal tight junctions. We hypothesized that enteral administration of sodium butyrate (NaB) in preweaned rats would result in differences in the development of diabetes associated with decreased infla...

Background: The intestinal epithelium is a barrier that composes one of the most immunologically active surfaces of the body due to constant exposure to microorganisms as well as an infinite diversity of food antigens. Disruption of intestinal barrier function and aberrant mucosal immune activation have been implicated in a variety of diseases wit...

Although it is known that resident gut flora contribute to immune system function and homeostasis, the role of gut flora in the progression of autoimmune disease is poorly understood. It has recently been shown that distinct bacterial populations are present within rodent models prone (DP) and resistant (DR) to Type 1 Diabetes (T1D). Oral Transfer...

An essential symbiotic relationship exists between intestinal cells and commensal bacteria within the human gastrointestinal tract. Alteration or absence of this interaction may play a role in the development of human disease. Use of probiotic organisms has yielded improvement of certain medical conditions, such as inflammatory and infectious gastr...

To use high throughput techniques to analyze intestinal microbial ecology in premature neonates, who are highly susceptible to perturbations of the luminal environment associated with necrotizing enterocolitis (NEC) and late-onset sepsis. With non-culture-based techniques, we evaluated intestinal microbiota shortly after birth and during hospitaliz...

Lactobacillus rhamnosus GG (LGG), a probiotics, ameliorates intestinal and other organ inflammation in infant rats. The hypothesis is that live and heat-killed LGG have similar effects on decreasing the inflammatory response induced by E. coli lipopolysaccharide (LPS) in the infant rat. Using a gastrostomy-fed rat model, 7-d-old rat pups were gastr...

Bacteria associated with the onset of type 1 diabetes in a rat model system were identified. In two experiments, stool samples were collected at three time points after birth from bio-breeding diabetes-prone (BB-DP) and bio-breeding diabetes-resistant (BB-DR) rats. DNA was isolated from these samples and the 16S rRNA gene was amplified using univer...

Glutamine (Gln) is important for intestinal barrier function and regulation of tight junction (TJ) proteins, but the intracellular mechanisms of action remain undefined. The purpose of this study was to test the hypothesis that Gln regulates intercellular junction integrity and TJ proteins through the phosphatidylinositol 3-kinase (PI3K)/Akt pathwa...

Early postnatal nutrition is involved in metabolic programming. Small for gestational age and premature babies commonly receive insufficient dietary protein during the neonatal period due to nutrition intolerance, whereas high protein formulas are used to achieve catch up growth. Neither the short term, nor the long term effects of such manipulatio...

Probiotics are widely used in the treatment and prevention of gastrointestinal problems. However, in some immune-compromised populations, the administration of live microorganisms may not be appropriate. A potential alternative to live microorganisms is to inactivate them as long as the beneficial function is retained. We hypothesized that UV-inact...

Neonatal diet may influence the development of type 1 diabetes (T1D) in susceptible individuals through an intestinal mucosal inflammatory response, resulting in loss of self-tolerance. We tested the hypothesis that formula feeding during the neonatal period accelerates the development of T1D in diabetes-prone BioBreeding (BBDP) rats through regula...

The potential efficacy of glutamine and glutamate as nutritional supplements for premature infants was originally met with enthusiasm. Despite no evidence of toxicity in the clinical trials, the use of glutamine has not become routine. In certain studies, the benefits seem clear, whereas in others, benefits have not been demonstrated. Specific desi...

Premature infants undergoing intensive care are highly vulnerable to amino acid deprivation. Supplementation of glutamine or arginine has resulted in beneficial effects in human neonates. This study was conducted to examine the effect of the dipeptide arginyl-glutamine (Arg-Gln) on vascular endothelial cell growth factor (VEGF) levels in primary hu...

A gastrostomy-fed rat infant "pup-in-a-cup" model was used to test the hypothesis that enterally administered Lactobacillus rhamnosus GG (LGG) decreases the proinflammatory response induced by Escherichia coli lipopolysaccharide (LPS) in the developing infant rat small intestine, plasma, lung and liver. Two groups of 6- to 7-day-old pups were fed a...

Interactions of resident intestinal microbes with the luminal contents and the mucosal surface play important roles in normal intestinal development, nutrition, and innate and adaptive immunity. The neonate, especially the premature, who possesses a highly immunoreactive intestinal submucosa underlying a single layer of epithelial cells that are co...

Certain probiotic bacteria show anti-inflammatory activity after being heat killed, whereas others do not, suggesting that the gastrointestinal environment may alter the activity of probiotic bacteria. Occasionally, probiotics are provided when a patient is also being treated with oral antibiotics; this may have an effect on the probiotic activity....

Type 1 diabetes is an autoimmune disorder that occurs in genetically susceptible individuals. It has been hypothesized that the disease could be triggered by environmental agents that gain entry into the body through small intestinal absorption. Increased intestinal permeability has been reported both in spontaneous animal models of type 1 diabetes...

The intestinal epithelium may serve as a nidus for inflammation that can cause local and systemic organ dysfunction. Relative to the adult, the immature intestine is exquisitely sensitive to inflammatory agents. Glutamine (Gln), an amino acid that is rapidly depleted during critical illness, modulates intestinal inflammation in vitro and in vivo. H...

Intestinal epithelial tight junction (TJ) barrier dysfunction may lead to inflammation and mucosal injury. Glutamine (GLN) plays a role in maintenance of intestinal barrier function in various animal models and critically ill humans. Recent evidence from intestinal cell monolayers indicates that GLN maintains transepithelial resistance and decrease...

Artificial rearing of rat pups has been used in the investigation of the neonatal gut. We propose to adapt the model of artificially rearing rat pups for use in mouse pups, thereby allowing the use of transgenic animals for our research. We hypothesized that gastrostomy catheters may be placed successfully into neonatal mouse pups and that the pups...

Objectives Critically ill neonates often have their enteral intake severely limited shortly after birth. Whether glutamine (Gln) or glutamate (Glu) can preserve intestinal structure and function in the neonate undergoing limited enteral feeding is not clear. We hypothesize that Gln and Glu can similarly preserve intestinal structure in the developi...

Critically ill neonates often have their enteral intake severely limited shortly after birth. Whether glutamine (Gln) or glutamate (Glu) can preserve intestinal structure and function in the neonate undergoing limited enteral feeding is not clear. We hypothesize that Gln and Glu can similarly preserve intestinal structure in the developing small in...

Using a gastrostomy-fed (GF) rat infant "pup-in-a-cup" model, the effects of protein deprivation and supplemental glutamine (Gln) and glutamate (Glu) were examined to test the hypothesis that Gln decreases the proinflammatory response induced by LPS in the developing infant rat small intestine. Four groups of 6- to 7-day-old pups were fed a rat mil...

The mechanism of glutamine (Gln)-mediated down-regulation of inflammation in the intestine is poorly understood. We hypothesize that Gln down-regulates lipopolysaccharide (LPS)-stimulated IL-8 production in intestinal epithelial cells via transcription factors that counteract the effect of LPS-mediated increase in IL-8. Caco-2 cells were incubated...

Glutamine (Gln) is important for intestinal epithelial proliferation. The purpose of this study was to determine whether glutamate (Glu), a mixture of nucleotide monophosphates, arginine, or glucosamine could support proliferation of rat intestinal crypt cells (IEC-6) in the absence of Gln. Glu with added ammonia acetate, glucosamine, arginine, and...

Recent evidence suggests that the conditionally essential amino acid glutamine is important for intestinal barrier function. However, the mechanism remains undefined. To determine the effects of glutamine on permeability of intestinal epithelial cell monolayers, Caco-2 cells were grown on membrane filters and exposed to 4 mmol/L sodium butyrate in...

Dietary glutamine (Gln) has been shown to be important for maintenance of the intestinal barrier. To investigate the role of the epithelium in this Gln dependence, Caco-2 cells were raised on semipermeable membranes under conditions that model different regions of the crypt and villus. Gln availability was controlled by addition to the medium and t...

Glutamine (Gln) supplementation has been shown to decrease production of pro-inflammatory cytokines by the human intestinal mucosa. The mechanism of this is poorly understood. We hypothesize that Gln down-regulates lipopolysaccharide (LPS)-stimulated pro-inflammatory cytokine production in Caco-2 cells by nuclear factor-kappa B (NF-kappaB). Caco-2...

Supplementation of the conditionally essential amino acid glutamine may be beneficial for individuals who are highly stressed and have minimal energy and protein reserves. This includes elderly individuals, postoperative patients, individuals with cancer and very low birthweight infants. Individuals who are undergoing treatment with catabolic gluco...