Probiotic Strain Lactobacillus Rhamnosus GG Research Articles

<i>In Vitro</i> Comparison of Probiotic Properties of <i>Lactobacillus fermentum</i> SK54 Isolated from New Born Baby with <i>Lactobacillus rhamnosus</i> GG ATCC 53103

A lactobacillus strain isolated from the feces of a healthy baby was identified as Lactobacillus fermentum SK54. The probiotic properties of this strain including antimicrobial activity, survival in acid, bile, simulated gastric fluid [SGF] and simulated intestinal fluid [SIF], antibiotic susceptibility and adherence to Caco-2 cells were examined and compared them with a well known commercial probiotic strain Lactobacillus rhamnosus GG ATCC 53103 isolated from human intestine. L. fermentum SK54 and L. rhamnosus GG showed inhibitory properties toward gastrointestinal pathogens i.e., Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella Typhimurium, and Shigella sonnei by cylinder-plate assay. The inhibitory substances from L. fermentum SK54 composed of acid substances naturally produced by lactobacilli and high molecular weight proteinaceous compound [MW > 3.5 kDa] which sensitive to proteolytic enzymes, pH stability [pH 2.0-5.0] and heat stability [60, 80, 100°C for 10 min and 121°C for15 min]. L. rhamnosus GG produced only acid inhibitory substances. Both strains survived well at low pH [pH 2.0-4.0], bile salts [0.1-0.3% w/v], SGF and SIF. They also had the same 14 tested antibiotic sensitivity pattern and expressed high adherence to Caco-2 cells. This study provides a rationale to support L. fermentum SK54 as a potential probiotic to prevent or act as a therapeutic agent against pathogenic strains.

SURVIVING OF COMMERCIAL PROBIOTIC STRAIN Lactobacillus rhamnosus GG IN SLOVAK COW LUMP CHEESE EXPERIMENTALLY INOCULATED WITH Listeria innocua

Cow lump cheese represents a traditional Slovak cheese. It belongs to fresh types of cheeses. The aim of this study was to test surviving of commercial probiotic strain Lactobacillus rhamnosus GG in cow lump cheese experimentally infected with L. innocua; (listeriae are contaminants) and to check the suitability of GG strain as additive for this product. The counts of GG strain in cow lump cheeses were well balanced during whole experiment. It was found in the counts from 5.48 ± 0.15 to 7.77 ±1.50 log10 cfu/g. Its maximum in cheese was 7.77 ± 1.30 log10 cfu/g on day 7 with stability up to day 14. The identity of GG strain isolated from cheeses was confirmed by PCR. The counts of other lactic acid bacteria were also well balanced during the whole experiment in the experimental cheeses with stability up to day 14. Only in E1/GG cheese, the highest number of LAB was detected (10.60 ±1.26 log10 cfu/g). The count of L. innocua LMG 13568 was not influenced. The pH and lactic acid values were not negatively influenced. Visually, the GG cheese provided a good structure (consistency).It can be disputed that shelf-life of the product could be maintained by this way and/or the product itself with GG strain can be consumed as afunctional food or to serve as a probiotic strain carrier.

Lactobacillus rhamnosus GG Protects against Non-Alcoholic Fatty Liver Disease in Mice

ObjectiveExperimental evidence revealed that obesity-associated non-alcoholic fatty liver disease (NAFLD) is linked to changes in intestinal permeability and translocation of bacterial products to the liver. Hitherto, no reliable therapy is available except for weight reduction. Within this study, we examined the possible effect of the probiotic bacterial strain Lactobacillus rhamnosus GG (LGG) as protective agent against experimental NAFLD in a mouse model.MethodsExperimental NAFLD was induced by a high-fructose diet over eight weeks in C57BL/J6 mice. Fructose was administered via the drinking water containing 30% fructose with or without LGG at a concentration resulting in approximately 5×107 colony forming units/g body weight. Mice were examined for changes in small intestinal microbiota, gut barrier function, lipopolysaccharide (LPS) concentrations in the portal vein, liver inflammation and fat accumulation in the liver.ResultsLGG increased beneficial bacteria in the distal small intestine. Moreover, LGG reduced duodenal IκB protein levels and restored the duodenal tight junction protein concentration. Portal LPS (P≤0.05) was reduced and tended to attenuate TNF-α, IL-8R and IL-1β mRNA expression in the liver feeding a high-fructose diet supplemented with LGG. Furthermore liver fat accumulation and portal alanine-aminotransferase concentrations (P≤0.05) were attenuated in mice fed the high-fructose diet and LGG.ConclusionsWe show for the first time that LGG protects mice from NAFLD induced by a high-fructose diet. The underlying mechanisms of protection likely involve an increase of beneficial bacteria, restoration of gut barrier function and subsequent attenuation of liver inflammation and steatosis.

Preliminary evaluation of probiotic properties of Lactobacillus strains isolated from Sardinian dairy products.

Twenty-three Lactobacillus strains of dairy origin were evaluated for some functional properties relevant to their use as probiotics. A preliminary subtractive screening based on the abilities to inhibit the growth of microbial pathogens and hydrolyze conjugated bile salts was applied, and six strains were selected for further characterization including survival under gastrointestinal environmental conditions, adhesion to gut epithelial tissue, enzymatic activity, and some safety properties. All selected strains maintained elevated cell numbers under conditions simulating passage through the human gastrointestinal tract, well comparable to the values obtained for the probiotic strain Lactobacillus rhamnosus GG, and were able to adhere to Caco-2 cells to various extents (from 3 to 20%). All strains exhibited high aminopeptidase, and absent or very low proteolytic and strong β-galactosidase activities; none was found to be haemolytic or to produce biogenic amines and all were susceptible to tetracycline, chloramphenicol, erythromycin, ampicillin, and amoxicillin/clavulanic acid. Our results indicate that the Lactobacillus strains analyzed could be considered appropriate probiotic candidates, due to resistance to GIT simulated conditions, antimicrobial activity, adhesion to Caco-2 cell-line, and absence of undesirable properties. They could be used as adjunct cultures for contributing to the quality and health related functional properties of dairy products.

Suitability of cereal porridges as substrate for probiotic strain Lactobacillus rhamnosus GG

The aim of this work was to find new substrates suitable for growth and metabolism of probiotic strain Lactobacillus rhamnosus GG, which would be interesting for development of new functional food. The growth and metabolic activity of Lb. rhamnosus GG in cereal (rye, barley, oat and millet) porridges were monitored during fermentation process. Cereal and porridges, were inoculated with this strain at two initial levels to obtain approximately 5 or 6 log colony form units per gram of suspension after sterilization and cooling,. Fermentation was led stationary at 37 °C for 48 hours and viable cell count, pH value, titratable acidity and organic acids were analysed. Metabolic activity of Lb. rhamnosus GG was influenced by inoculation level and by the type of cereal used. The cereals fermented by lactic acid bacteria, especially probiotic strains, might broaden the offer of probiotic products for those suffering from milk allergy.

Probiotic strains Lactobacillus plantarum 299V and Lactobacillus rhamnosus GG as starter cultures for fermented sausages

Probiotic food products are a fast growing area. Although probiotic strains are currently used in dairy products, their commercial application in fermented meat products is not yet common. The aim of this study was to assess the competitiveness of two probiotic Lactobacillus strains (Lactobacillus plantarum 299V and Lactobacillus rhamnosus GG) during the manufacture of Spanish fermented sausages and their effect on the hygienic and sensory qualities of the final products. The inoculated strains were successfully monitored by Randomly Amplified Polymorphic DNA (RAPD)-PCR. Both strains prevented the growth of Enterobacteriaceae throughout the entire ripening process. L. rhamnosus GG and L. plantarum 299V at high inoculum (ca. 107 CFU/g) produced a sharp decrease of pH values and low growth of Gram-positive Catalase-positive Cocci (GCC+), leading to a negative effect on the sensory attributes evaluated. Nevertheless, L. plantarum 299V inoculated at 105 CFU/g achieved and maintained high counts until the end of ripening and storage (ca.108 CFU/g), co-dominating (60%) with the endogenous microbiota, producing functional sausages with a satisfactory overall sensory quality. No major differences in physico-chemical parameters or sensory attributes were recorded when compared to spontaneously fermented sausages, thus adding further value to this type of meat product as a probiotic vehicle.

Evaluation of Cereals and Pseudocereals Suitability for the Development of New Probiotic Foods

The aim of the present work was to evaluate suitability of cereals and pseudocereals for the development of new probiotic foods and to evaluate the stability of cereal and pseudocereal porridges fermented by probiotic strain Lactobacillus rhamnosus GG. Ten samples of cereals and pseudocereals obtained from Slovak mill house and markets were used in this work. A mixture of each cereal and pseudocereal samples with water (10% w/v) was inoculated after sterilization with coequal number of Lactobacillus rhamnosus GG, to obtain approximately 5‐6 log colony form units per gram of suspensions. Fermentation was led at 37°C during 10 hours. Fermented suspensions were stored for 21 days at 5°C. Monitoring of cell counts, pH value, and concentration of organic acids during fermentation and storage was done.

Influence of fermentation conditions on the surface properties and adhesion of Lactobacillus rhamnosus GG

BackgroundThe surface properties of probiotic bacteria influence to a large extent their interactions within the gut ecosystem. There is limited amount of information on the effect of the production process on the surface properties of probiotic lactobacilli in relation to the mechanisms of their adhesion to the gastrointestinal mucosa. The aim of this work was to investigate the effect of the fermentation pH and temperature on the surface properties and adhesion ability to Caco-2 cells of the probiotic strain Lactobacillus rhamnosus GG.ResultsThe cells were grown at pH 5, 5.5, 6 (temperature 37°C) and at pH 6.5 (temperature 25°C, 30°C and 37°C), and their surfaces analysed by X-ray photoelectron spectrometry (XPS), Fourier transform infrared spectroscopy (FT-IR) and gel-based proteomics. The results indicated that for all the fermentation conditions, with the exception of pH 5, a higher nitrogen to carbon ratio and a lower phosphate content was observed at the surface of the bacteria, which resulted in a lower surface hydrophobicity and reduced adhesion levels to Caco-2 cells as compared to the control fermentation (pH 6.5, 37°C). A number of adhesive proteins, which have been suggested in previous published works to take part in the adhesion of bacteria to the human gastrointestinal tract, were identified by proteomic analysis, with no significant differences between samples however.ConclusionsThe temperature and the pH of the fermentation influenced the surface composition, hydrophobicity and the levels of adhesion of L. rhamnosus GG to Caco-2 cells. It was deduced from the data that a protein rich surface reduced the adhesion ability of the cells.

Interaction of Campylobacter spp. and Human Probiotics in Chicken Intestinal Mucus

Campylobacter is the most common cause of bacterial food-borne diarrhoeal disease throughout the world. The principal risk of human contamination is handling and consumption of contaminated poultry meat. To colonize poultry, Campylobacter adheres to and persists in the mucus layer that covers the intestinal epithelium. Inhibiting adhesion to the mucus could prevent colonization of the intestine. The aim of this study was to investigate in vitro the protective effect of defined commercial human probiotic strains on the adhesion of Campylobacter spp. to chicken intestinal mucus, in a search for alternatives to antibiotics to control this food-borne pathogen. The probiotic strains Lactobacillus rhamnosus GG and Propionibacterium freudenreichii ssp. shermanii JS and a starter culture strain Lactococcus lactis ssp. lactis adhered well to chicken intestinal mucus and were able to reduce the binding of Campylobacter spp. when the mucus was colonized with the probiotic strain before contacting the pathogen. Human-intended probiotics could be useful as prophylactics in poultry feeding for controlling Campylobacter spp. colonization.

An Evaluation of the Ability of the Probiotic Strain Lactobacillus rhamnosus GG to Eliminate the Gastrointestinal Carrier State of Vancomycin-resistant Enterococci in Colonized Children

To evaluate the efficacy of Lactobacillus rhamnosus GG (LGG) supplementation in eliminating the gastrointestinal carrier state of vancomycin-resistant enterococci (VRE) in colonized children, and to evaluate the affect of the probiotic on Lactobacillus spp. counts in the gastrointestinal tract. A randomized, single-blind, placebo-controlled study. Children (0 to 18 y old) hospitalized at the wards of the children's hospital who were diagnosed with gastrointestinal carrier state of VRE were randomized to group receiving 3 billion colony forming unit of LGG/day or placebo for 21 consecutive days. A total of 61 children completed the study (32 in the treatment group and 29 in the control group). Rectal swabs for VRE and Lactobacillus spp. were collected at baseline, during supplementation at weekly intervals and 1 month after supplementation. Antibiotic supply was controlled throughout the duration of the analysis. A significant difference in the number of children colonized with VRE between the groups was observed at 3 weeks (P = 0.002). The VRE carrier state was lost by 20 of 32 participants in the treatment group and 7 of 29 in the control group. We also observed increased gastrointestinal counts of Lactobacillus spp. in children receiving LGG. A statistically significant difference in the occurrence of bacteria was observed from week 1 onwards, whereas in the aspect of growth intensity from week 2 onwards. LGG supplementation temporarily eliminates the VRE carrier state and increases gastrointestinal counts of Lactobacillus spp. in children versus placebo.

91 Can Postnatal Supplementation with Probiotics Reduce the Risk for Allergic Disease in Infancy?

Background and aims: The increasing allergy prevalence may depend on a reduced microbial exposure early in life. Probiotics may prevent eczema in infants. Prenatal maternal supplementation might be crucial for this effect. The mixture of probiotic strains used in the present study reduced eczema when previously supplemented both pre- and postnatally. The aim of this study was to evaluate the effect of only postnatal probiotic supplementation on allergic manifestations during the first two years of life and to explore the impact of environmental factors on allergy development.Methods: In the double-blind placebo-controlled PRODIA study, infants with HLA risk genotype for type 1 diabetes were supplemented from two until six months of age with placebo or the probiotic strains Lactobacillus rhamnosus GG, Lactobacillus rhamnosus LC705, Bifidobacterium breve Bbi99 and Propionibacterium freudenreichii ssp. Shermani JS. 177 of the families completed questionnaires addressing allergy development until two years of age.Results: The cumulative incidence of eczema was not significantly different in the probiotic (21.7%) and the placebo group (14.1%). Children receiving probiotics, as compared with placebo, had a lower cumulative incidence of wheeze, 34.1% versus 49.4% (p=0.04). Children attending day-care had a lower cumulative incidence of eczema (p=0.03). Recurrent wheeze was associated with treatment with antibiotics (p=0.005) and care in the neonatal ward (p=0.02).Conclusion: Postnatal probiotic supplementation did not affect the development of infant eczema in children with genetic risk for diabetes, but showed association with a lower incidence of wheeze. Allergy development was associated with environmental factors potentially modulating microbial load.

Adaptation factors of the probiotic Lactobacillus rhamnosus GG

Probiotic bacteria are administered as live micro-organisms to provide a health benefit to the host. Knowledge on adaptation factors that promote the survival and persistence of probiotics in the intestine is key to understand and improve their ecological and probiotic performance. Adaptation factors include adhesins, molecules conferring stress tolerance and nutritional versatility, antimicrobial products against competing microbes, and factors promoting resistance against the host immune system. Here, we present an overview of the current knowledge on adaptation factors of probiotic lactobacilli, with focus on the prototypical and widely documented probiotic strain Lactobacillus rhamnosus GG.

Effects of Lactobacillus rhamnosus GG on saliva-derived microcosms

Objective The probiotic strain Lactobacillus rhamnosus GG (LGG) is shown to hamper the presence of mutans streptococci in saliva and may have positive effects on oral health. We investigated the effects of LGG on the cariogenic potential and microbial composition of saliva-derived microcosms. Design Single and dual species biofilms of LGG and Streptococcus mutans, and saliva-derived microcosms with or without LGG were grown in an Active Attachment Biofilm model. The microcosms were grown on bovine dentin/enamel discs in the presence or absence of sucrose (suc+/suc−). The presence of LGG was determined by multiplex ligation-dependent probe amplification (MLPA) and real-time PCR. Mutans streptococci (MS) and total viable counts, pH of the spent medium, capacity of lactate formation and integrated mineral loss in dentin was assessed. MLPA was used for identification and relative quantification of 20 oral microorganisms in the microcosms. Principal Component Analysis was applied to MLPA data. Results LGG inhibited the growth of S. mutans in dual species biofilms and did not affect the pH. LGG established in saliva-derived microcosms and reduced MS counts significantly, but did not affect pH or dentin demineralization. Simultaneous growth of the microcosms with LGG under heavy cariogenic conditions (suc+) introduced a compositional shift in the microbial community. The CFU, real-time PCR and MLPA data correlated significantly. Conclusion We conclude that LGG established into and inhibited the growth of MS in complex saliva-derived biofilms, but this had no significant effect on cariogenic potential of the microcosms. This suggests that other microorganisms besides MS were responsible for increased cariogenicity of sucrose-exposed biofilms.

Probiotic Lactobacilli Interfere with Streptococcus mutans Biofilm Formation In Vitro

In clinical studies, probiotic bacteria have decreased the counts of salivary mutans streptococci (MS). We compared the effects of probiotic Lactobacillus strains on the biofilm formation of Streptococcus mutans. The bacterial strains used included four S. mutans strains (reference strains NCTC 10449 and Ingbritt and clinical isolates 2366 and 195) and probiotic strains Lactobacillus rhamnosus GG, L. plantarum 299v, and L. reuteri strains PTA 5289 and SD2112. The ability of MS to adhere and grow on a glass surface, reflecting biofilm formation, was studied in the presence of the lactobacilli (LB). The effect of LB culture supernatants on the viability of the MS was studied as well. All of the LB inhibited the biofilm formation of the clinical isolates of MS (P < 0.001). The biofilm formation of the reference strains of MS was also inhibited by the LB, but L. plantarum and L. reuteri PTA 5289 showed a weaker inhibition when compared to L. reuteri SD2112 and L. rhamnosus GG. Viable S. mutans cells could be detected in the biofilms and culture media only when the experiments were performed with the L. reuteri strains. The L. reuteri strains were less efficient in killing the MS also in the tests performed with the culture supernatants. The pHs of the supernatants of L. reuteri were higher compared to those of L. rhamnosus GG and L. plantarum; P < 0.001. In conclusion, our results demonstrated that four commonly used probiotics interfered with S. mutans biofilm formation in vitro, and that the antimicrobial activity against S. mutans was pH-dependent.

Microbiological and physicochemical quality of fresh-cut apple enriched with the probiotic strain Lactobacillus rhamnosus GG

The effectiveness as protective culture of the probiotic Lactobacillus rhamonosus GG ( L. rham. GG) against Salmonella and Listeria monocytogenes on minimally-processed apples throughout storage as well as its effect on apple quality and natural microflora was evaluated. Survival to subsequent exposure to gastric stress was also reported. Apples were cut into wedges and dipped in a solution containing Salmonella and L. monocytogenes (10 5 cfu mL −1) and/or L. rham. GG (10 8 cfu mL −1). Apple wedges were packed and stored at 5 and 10 °C. Periodically, microbial population, bacterial survival to gastric stress and quality of apple wedges were evaluated. Although Salmonella was not affected by co-inoculation with L. rham. GG, L. monocytogenes population was 1-log units lower in the presence of L. rham. GG. L. rham. GG population maintained over recommended levels for probiotic action (10 6 cfu g −1) along storage, however, viable cells after gastric stress were only above this level during the first 14 days. Pathogen survival after gastric stress was <1% after 7 days at 5 °C. Moreover, apple wedges quality was not affected by L. rham. GG addition. Thus, L. rham. GG could be a suitable probiotic for minimally-processed apples capable to reduce L. monocytogenes growth; nevertheless shelf life should not be higher to 14 days to guarantee the probiotic effect.

Exopolysaccharides of Lactobacillus rhamnosus GG form a protective shield against innate immune factors in the intestine

SummaryProbiotic bacteria are administered as live microorganisms to provide a health benefit to the host. Insight into the adaptation factors that promote the survival and persistence of probiotics in the gastrointestinal tract (GIT) is important to understand their performance. In this study, the role of the long galactose‐rich exopolysaccharides (EPS) of the prototypical probiotic strain Lactobacillus rhamnosus GG (LGG) was investigated. In a competition experiment with wild type, the isogenic EPS mutant CMPG5351 exhibited a reduced persistence in the murine GIT, especially in the lower parts of the intestine. This was surprising as our previous in vitro studies had shown an increased adhesion capacity for this EPS mutant. Follow‐up assays indicated that this mutant is more sensitive towards host innate defence molecules, such as the LL‐37 antimicrobial peptide and complement factors. This suggests that EPS forms a protective shield for LGG against these molecules in the GIT. Moreover, culturing LGG wild‐type in subinhibitory concentrations of host defence factors such as LL‐37 resulted in increased production of EPS, indicating that bacterial EPS production is modulated in the host to fine‐tune the balance between adhesion and immune evasion. These observations are of interest in understanding the dynamics of adaptation of probiotics to the host environments.

Lactobacilli stimulate the innate immune response and modulate the TLR expression of HT29 intestinal epithelial cells in vitro

The potentially probiotic strain Lactobacillus plantarum BFE 1685 isolated from a child's faeces and the probiotic strain Lactobacillus rhamnosus GG were investigated for their capability to influence the innate immune response of HT29 intestinal epithelial cells towards Salmonella enterica serovar Typhimurium. Furthermore, their capacity to modulate toll-like receptor expression of HT29 cells was investigated at the mRNA and protein levels. TNF-α was used in cell culture with HT29 cells to mimic an inflammatory background, and in the presence of this chemokine HT29 cells were sensitised to respond to the Lactobacillus strains as evidenced by an increased response in IL-8 production. In addition, when HT29 cells were first treated with lactobacilli and then infected with S. Typhimurium, the IL-8 levels in response to S. Typhimurium were significantly higher, indicating that HT29 cells were sensitised by lactobacilli. Neither of the lactobacilli was able to stimulate TLR4 production at the mRNA level, however, TLR2 and TLR9 transcription levels measured by quantitative PCR were up-regulated when HT29 cells were incubated with lactobacilli, but not with S. Typhimurium. Up-regulation of TLR9 expression was higher for L. rhamnosus GG than for L. plantarum BFE 1685. Expression levels of TLR2 and TLR5 were enhanced also at the protein level as determined by flow cytometry after staining with the respective antibodies. In contrast, TLR9 expression was not significantly up-regulated, which may be explained by protein degradation, or possible down-stream regulatory effects. These findings show that stimulation of specific signaling pathways occurs in the cross-talk between probiotic bacteria and gut epithelium cells, which can help to explain the adjuvant properties of probiotic lactobacilli.

Identification of a Gene Cluster for the Biosynthesis of a Long, Galactose-Rich Exopolysaccharide in Lactobacillus rhamnosus GG and Functional Analysis of the Priming Glycosyltransferase.

Cell surface polysaccharides have an established role as virulence factors in human bacterial pathogens. Less documented are the biosynthesis and biological functions of surface polysaccharides in beneficial bacteria. We identified a gene cluster that encodes the enzymes and regulatory and transporter proteins for the different steps in the biosynthesis of extracellular polysaccharides (EPS) of the well-documented probiotic strain Lactobacillus rhamnosus GG. Subsequent mutation of the welE gene, encoding the priming glycosyltransferase within this cluster, and comparative phenotypic analyses of wild-type versus mutant strains confirmed the specific function of this gene cluster in the biosynthesis of high-molecular-weight, galactose-rich heteropolymeric EPS molecules. The phenotypic analyses included monomer composition determination, estimation of the polymer length of the isolated EPS molecules, and single-molecule force spectroscopy of the surface polysaccharides. Further characterization of the welE mutant also showed that deprivation of these long, galactose-rich EPS molecules results in an increased adherence and biofilm formation capacity of L. rhamnosus GG, possibly because of less shielding of adhesins such as fimbria-like structures.

Atopic dermatitis: Therapeutic concepts evolving from new pathophysiologic insights

Recent insights into the relevance of the epidermal barrier function and its interaction with components of the innate and adaptive immune responses in patients with atopic dermatitis (AD) give rise to a number of novel potential treatment options. In particular, the identification of loss-of-function mutations in the barrier protein filaggrin and of a diminished expression of certain antimicrobial peptides in AD skin stimulates new concepts to think beyond the T(H)1/T(H)2 paradigm. This review will focus on these most recent discoveries and will discuss new and corresponding proof-of-concept trials in patients with AD. It will further speculate on novel ways to restore the homeostasis among the 3 major components in AD skin suspected to be clinically relevant.

Impact of luxS and Suppressor Mutations on the Gastrointestinal Transit of Lactobacillus rhamnosus GG

It is generally believed that probiotic bacteria need to survive gastrointestinal transit to exert a health-promoting effect. In this study, a genuine luxS mutant and a luxS mutant containing unknown suppressor mutations of the probiotic strain Lactobacillus rhamnosus GG were compared to the wild type for survival and persistence in the murine gastrointestinal tract. The LuxS enzyme, catalyzing the production of the autoinducer-2 signaling molecule, also forms an integral part of the activated methyl cycle and the metabolism of methionine and cysteine. The genuine luxS mutant CMPG5412 showed drastically reduced persistence in mice, which was related to less survival in simulated gastric juice, indicating that LuxS metabolism is crucial for the gastric stress resistance of L. rhamnosus GG. The suppressor mutations in the other luxS mutant, CMPG5413, appear to compensate for the metabolic defects of the luxS mutation and to restore the resistance to gastric juice but cause a defect in adherence, biofilm formation, and exopolysaccharide production. The shorter residence time of this suppressor mutant in the murine gastrointestinal tract indicates a role for biofilm formation and exopolysaccharides in the persistence capacity of L. rhamnosus GG.