The S-layer proteins of Lactobacillus crispatus strain ZJ001 is responsible for competitive exclusion against Escherichia coli O157:H7 and Salmonella typhimurium

Pre-treatment with Bifidobacterium breve UCC2003 modulates Citrobacter rodentium-induced colonic inflammation and organ specificity

Citrobacter rodentium, which colonizes the gut mucosa via formation of attaching and effacing (A/E) lesions, causes transmissible colonic hyperplasia. The aim of this study was to evaluate whether prophylactic treatment with Bifidobacterium breve UCC2003 can improve the outcome of C. rodentium infection. Six-week-old albino C57BL/6 mice were pre-treated for 3 days with B. breve, challenged with bioluminescent C. rodentium and administered B. breve or PBS-C for 8 days post-infection; control mice were either administered B. breve and mock-infected with PBS, or mock-treated with PBS-C and mock-infected with PBS. C. rodentium colonization was monitored by bacterial enumeration from faeces and by a combination of both 2D bioluminescence imaging (BLI) and composite 3D diffuse light imaging tomography with µCT imaging (DLIT-µCT). At day 8 post-infection, colons were removed and assessed for crypt hyperplasia, histology by light microscopy, bacterial colonization by immunofluorescence, and A/E lesion formation by electron microscopy. Prophylactic administration of B. breve did not prevent C. rodentium colonization or A/E lesion formation. However, this treatment did alter C. rodentium distribution within the large intestine and significantly reduced colonic crypt hyperplasia at the peak of bacterial infection. These results show that B. breve could not competitively exclude C. rodentium, but reduced pathogen-induced colonic inflammation.

Lactobacillus reuteri protects epidermal keratinocytes from Staphylococcus aureus-induced cell death by competitive exclusion

Recent studies have suggested that the topical application of probiotic bacteria can improve skin health or combat disease. We have utilized a primary human keratinocyte culture model to investigate whether probiotic bacteria can inhibit Staphylococcus aureus infection. Evaluation of the candidate probiotics Lactobacillus reuteri ATCC 55730, Lactobacillus rhamnosus AC413, and Lactobacillus salivarius UCC118 demonstrated that both L. reuteri and L. rhamnosus, but not L. salivarius, reduced S. aureus-induced keratinocyte cell death in both undifferentiated and differentiated keratinocytes. Keratinocyte survival was significantly higher if the probiotic was applied prior to (P < 0.01) or simultaneously with (P < 0.01) infection with S. aureus but not when added after infection had commenced (P > 0.05). The protective effect of L. reuteri was not dependent on the elaboration of inhibitory substances such as lactic acid. L. reuteri inhibited adherence of S. aureus to keratinocytes by competitive exclusion (P = 0.026). L. salivarius UCC118, however, did not inhibit S. aureus from adhering to keratinocytes (P > 0.05) and did not protect keratinocyte viability. S. aureus utilizes the α5β1 integrin to adhere to keratinocytes, and blocking of this integrin resulted in a protective effect similar to that observed with probiotics (P = 0.03). This suggests that the protective mechanism for L. reuteri-mediated protection of keratinocytes was by competitive exclusion of the pathogen from its binding sites on the cells. Our results suggest that use of a topical probiotic prophylactically could inhibit the colonization of skin by S. aureus and thus aid in the prevention of infection.

Characterization of a S-layer protein from Lactobacillus crispatus K313 and the domains responsible for binding to cell wall and adherence to collagen

It was previously shown that the surface (S)-layer proteins covering the cell surface of Lactobacillus crispatus K313 were involved in the adherence of this strain to human intestinal cell line HT-29. To further elucidate the structures and functions of S-layers, three putative S-layer protein genes (slpA, slpB, and slpC) of L. crispatus K313 were amplified by PCR, sequenced, and characterized in detail. Quantitative real-time PCR analysis reveals that slpA was silent under the tested conditions; whereas slpB and slpC, the putative amino acid sequences which exhibited minor similarities to the previously reported S-layer proteins in L. crispatus, were actively expressed. slpB, which was predominantly expressed in L. crispatus K313, was further investigated for its functional domains. Genetic truncation of the untranslated leader sequence (UTLS) of slpB results in a reduction in protein production, indicating that the UTLS contributed to the efficient S-layer protein expression. By producing a set of N- and C-terminally truncated recombinant SlpB proteins in Escherichia coli, the cell wall-binding region was mapped to the C terminus, where rSlpB(380-501) was sufficient for binding to isolated cell wall fragments. Moreover, the binding ability of the C terminus was variable among the Lactobacillus species (S-layer- and non-S-layer-producing strains), and teichoic acid may be acting as the receptor of SlpB. To determine the adhesion region of SlpB to extracellular matrix proteins, ELISA was performed. Binding to immobilized types I and IV collagen was observed with the His-SlpB(1-379) peptides, suggesting that the extracellular matrix protein-binding domain was located in the N terminus.

Antagonistic activity of Lactobacillus acidophilus ATCC 4356 on the growth and adhesion/invasion characteristics of human Campylobacter jejuni

The aim of this research was to determine the potential probiotic activity of Lactobacillus acidophilus ATCC 4356 against several human Campylobacter jejuni isolates. The ability to inhibit the pathogen's growth was evaluated by co-culture experiments as well as by antimicrobial assays with cell-free culture supernatant (CFCS), while interference with adhesion/invasion to intestinal Caco-2 cells was studied by exclusion, competition, and displacement tests. In the co-culture experiments L. acidophilus ATCC 4356 strain reduced the growth of C. jejuni with variable percentages of inhibition related to the contact time. The CFCS showed inhibitory activity against C. jejuni strains, stability to low pH, and thermal treatment and sensitivity to proteinase K and trypsin. L. acidophilus ATCC 4356 was able to reduce the adhesion and invasion to Caco-2 cells by most of the human C. jejuni strains. Displacement and exclusion mechanisms seem to be the preferred modalities, which caused a significant reduction of adhesion/invasion of pathogens to intestinal cells. The observed inhibitory properties of L. acidophilus ATCC 4356 on growth ability and on cells adhesion/invasion of C. jejuni may offer potential use of this strain for the management of Campylobacter infections.

Development of an innovative nutraceutical fermented beverage from herbal mate (Ilex paraguariensis A.St.-Hil.) extract

Herbal mate (Ilex paraguariensis A.St.-Hil.) leaves are traditionally used for their stimulant, antioxidant, antimicrobial, and diuretic activity, presenting as principal components polyphenolic compounds. The aim of this work was to develop an innovative, non-dairy, functional, probiotic, fermented beverage using herbal mate extract as a natural ingredient which would also be hypocholesterolemic and hepatoprotective. Among different strains used, Lactobacillus acidophilus was selected as the best for fermentation. The addition of honey positively affected the development of L. acidophilus and the formulated beverage maintained microbial stability during shelf life. Key ingredients in the extract included xanthines, polyphenols and other antioxidants with potential health benefits for the consumer. Caffeine levels and antioxidant activity were also studied. Acceptable levels of caffeine and large antioxidant capacity were observed for the formulation when compared to other antioxidant beverages. An advantage of this product is the compliance to organic claims, while providing caffeine, other phyto-stimulants and antioxidant compounds without the addition of synthetic components or preservatives in the formulation. Sensorial analysis demonstrated that the beverage had good consumer acceptance in comparison to two other similar commercial beverages. Therefore, this beverage could be used as a new, non-dairy vehicle for probiotic consumption, especially by vegetarians and lactose intolerant consumers. It is expected that such a product will have good market potential in an era of functional foods.

Recombinant probiotic expressing Listeria adhesion protein attenuates Listeria monocytogenes virulence in vitro

BACKGROUND

Listeria monocytogenes, an intracellular foodborne pathogen, infects immunocompromised hosts. The primary route of transmission is through contaminated food. In the gastrointestinal tract, it traverses the epithelial barrier through intracellular or paracellular routes. Strategies to prevent L. monocytogenes entry can potentially minimize infection in high-risk populations. Listeria adhesion protein (LAP) aids L. monocytogenes in crossing epithelial barriers via the paracellular route. The use of recombinant probiotic bacteria expressing LAP would aid targeted clearance of Listeria from the gut and protect high-risk populations from infection.

METHODOLOGY/PRINCIPAL FINDINGS

The objective was to investigate the ability of probiotic bacteria or LAP-expressing recombinant probiotic Lactobacillus paracasei (Lbp(LAP)) to prevent L. monocytogenes adhesion, invasion, and transwell-based transepithelial translocation in a Caco-2 cell culture model. Several wild type probiotic bacteria showed strong adhesion to Caco-2 cells but none effectively prevented L. monocytogenes infection. Pre-exposure to Lbp(LAP) for 1, 4, 15, or 24 h significantly (P<0.05) reduced adhesion, invasion, and transepithelial translocation of L. monocytogenes in Caco-2 cells, whereas pre-exposure to parental Lb. paracasei had no significant effect. Similarly, Lbp(LAP) pre-exposure reduced L. monocytogenes translocation by as much as 46% after 24 h. Lbp(LAP) also prevented L. monocytogenes-mediated cell damage and compromise of tight junction integrity. Furthermore, Lbp(LAP) cells reduced L. monocytogenes-mediated cell cytotoxicity by 99.8% after 1 h and 79% after 24 h.

CONCLUSIONS/SIGNIFICANCE

Wild type probiotic bacteria were unable to prevent L. monocytogenes infection in vitro. In contrast, Lbp(LAP) blocked adhesion, invasion, and translocation of L. monocytogenes by interacting with host cell receptor Hsp60, thereby protecting cells from infection. These data show promise for the use of recombinant probiotics in preventing L. monocytogenes infection in high-risk populations.

Probiotic lactic acid bacteria in the gastro-intestinal tract: health benefits, safety and mode of action

Lactic acid bacteria (LAB) have received considerable attention as probiotics over the past few years. This concept has grown from traditional dairy products to a profitable market of probiotic health supplements and functional foods. Extensive research is done on novel potential probiotic strains, with specific emphasis on their health benefits and mode of action. Criteria for the selection of probiotic strains have only recently been formulated by the Food and Agriculture Organization of the United Nations and the World Health Organization (FAO/WHO). Several in vitro techniques have been developed to evaluate the probiotic properties of strains. In many cases, this is followed by in vivo tests. Safety studies are also obligatory, as a few cases of bacteremia caused by LAB have been reported. This review focuses on the health benefits and safety of LAB probiotics, the criteria used to select a probiotic, mode of action and the impact these organisms have on natural microbiota in the gastro-intestinal tract.

Lactobacillus S-layer protein inhibition of Salmonella-induced reorganization of the cytoskeleton and activation of MAPK signalling pathways in Caco-2 cells

Surface layer (S-layer) proteins are crystalline arrays of proteinaceous subunits that are present as the outermost component of the cell wall in several Lactobacillus species. The S-layer proteins have been shown to play a role in the antimicrobial activity of certain lactobacilli. However, it is not fully understood how the S-layer proteins exert this biological function. The aim of this study was to test the hypothesis that Lactobacillus acidophilus S-layer proteins antagonize Salmonella Typhimurium (S. Typhimurium) infection by protecting against F-actin cytoskeleton rearrangements and the activation of mitogen-activated protein kinase (MAPK) signalling pathways. Monolayer transepithelial electrical resistance (TER) was measured after S. Typhimurium infection in Caco-2 cultured human intestinal cells with L. acidophilus S-layer proteins. F-actin rearrangement and MAPK activation were also assessed by immunofluorescence staining or Western blotting. The results showed that when S. Typhimurium was co-incubated with S-layer proteins, the S. Typhimurium-induced Caco-2 cell F-actin rearrangement was reduced, and the S. Typhimurium-induced TER decrease and interleukin 8 (IL-8) secretion were attenuated. Additionally, L. acidophilus S-layer proteins could inhibit S. Typhimurium-induced phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun amino-terminal kinase (JNK) and p38. This study indicates that L. acidophilus S-layer proteins are able to inhibit S. Typhimurium infection through blocking S. Typhimurium-induced F-actin rearrangements and S. Typhimurium-induced ERK1/2, JNK and p38 activation in Caco-2 cells. These data provide a rationale for the use of lactobacillus S-layer proteins as therapeutic and preventative agents, at least in infectious diarrhoea.

Effect of dietary supplementation with a Saccharomyces cerevisiae mannan oligosaccharide on the bacterial community structure of broiler cecal contents

This study investigated the effects of dietary supplementation with a prebiotic mannan oligosaccharide (MOS) on broiler performance, bacterial community structure, and phylogenetic populations of cecal contents. Bird performance data were collected, and cecal samples were extracted from randomly caught poults from each treatment group every 7 days from hatching to the age of 42 days. Weight gain, feed consumption, and feed efficiency ratios did not differ significantly between groups. Automated ribosomal intergenic spacer analysis (ARISA) of the bacterial communities in birds receiving MOS-supplemented diets indicated that dietary supplementation with MOS at either of 2 levels significantly altered the bacterial community structure from that of the control group on all sample days. The phylogenetic identities of bacteria contained within the cecum were determined by constructing a 16S rRNA gene clone library. A total of 594 partial 16S rRNA gene sequences from the cecal contents were analyzed and compared for the three dietary treatments. The dominant bacteria of the cecum belonged to three phyla, Firmicutes, Bacteroidetes, and Proteobacteria; of these, Firmicutes were the most dominant in all treatment groups. Statistical analysis of the bacterial 16S rRNA gene clone libraries showed that the compositions of the clone libraries from broilers receiving MOS-supplemented diets were, in most cases, significantly different from that of the control group. It can be concluded that in this trial MOS supplementation significantly altered the cecal bacterial community structure.

The starting lineup: key microbial players in intestinal immunity and homeostasis

The complexity of microbiota inhabiting the intestine is increasingly apparent. Delicate balance of numerous bacterial species can affect development of the immune system, how susceptible a host is to pathogenic organisms, and the auto-inflammatory state of the host. In the last decade, with the increased use of germ-free mice, gnotobiotic mice, and animal models in which a germ-free animal has been colonized with a foreign microbiota such as humanized mice, it has been possible to delineate relationships that specific bacteria have with the host immune system and to show what role they may play in overall host health. These models have not only allowed us to tease out the roles of individual species, but have also allowed the discovery and characterization of functionally unknown organisms. For example, segmented filamentous bacteria (SFB) have been shown to play a vital role in expansion of IL-17 producing cells. Prior to linking their key role in immune system development, little was known about these organisms. Bacteroides fragilis can rescue some of the immune defects of gnotobiotic mice after mono-colonization and have anti-inflammatory properties that can alleviate colitis and experimental allergic encephalitis in murine models. Additionally, Clostridium species have most recently been shown to expand regulatory T-cell populations leading to anti-inflammatory conditions. This review will highlight and summarize some of the major findings within the last decade concerning the role of select groups of bacteria including SFB, Clostridium, Bacteroides, Bifidobacterium, and Lactobacillus, and their impact on host mucosal immune systems.

Review: The use of direct fed microbials to mitigate pathogens and enhance production in cattle

McAllister, T. A., Beauchemin, K. A., Alazzeh, A. Y., Baah, J., Teather, R. M. and Stanford, K. 2011. Review: The use of direct fed microbials to mitigate pathogens and enhance production in cattle. Can. J. Anim. Sci. 91: 193–211. Direct-fed microbials (DFM) have been employed in ruminant production for over 30 yr. Originally, DFM were used primarily in young ruminants to accelerate establishment of the intestinal microflora involved in feed digestion and to promote gut health. Further advancements led to more sophisticated mixtures of DFM that are targeted at improving fiber digestion and preventing ruminal acidosis in mature cattle. Through these outcomes on fiber digestion/rumen health, second-generation DFM have also resulted in improvements in milk yield, growth and feed efficiency of cattle, but results have been inconsistent. More recently, there has been an emphasis on the development of DFM that exhibit activity in cattle against potentially zoonotic pathogens such as Escherichia coli O157:H7, Salmonella spp. and Staphylococcus aureus. Regulatory requirements have limited the microbial species within DFM products to organisms that are generally recognized as safe, such as lactic acid-producing bacteria (e.g., Lactobacillus and Enterococcus spp.), fungi (e.g., Aspergillus oryzae), or yeast (e.g., Saccharomyces cerevisiae). Direct-fed microbials of rumen origin, involving lactate-utilizing species (e.g., Megasphaera elsdenii, Selenomonas ruminantium, Propionibacterium spp.) and plant cell wall-degrading isolates of Butyrivibrio fibrisolvens have also been explored, but have not been commercially used. Development of DFM that are efficacious over a wide range of ruminant production systems remains challenging because[0] comprehensive knowledge of microbial ecology is lacking. Few studies have employed molecular techniques to study in detail the interaction of DFM with native microbial communities or the ruminant host. Advancements in the metagenomics of microbial communities and the genomics of microbial–host interactions may enable DFM to be formulated to improve production and promote health, responses that are presently often achieved through the use of antimicrobials in cattle.

Lactobacillus adhesion to mucus

Mucus provides protective functions in the gastrointestinal tract and plays an important role in the adhesion of microorganisms to host surfaces. Mucin glycoproteins polymerize, forming a framework to which certain microbial populations can adhere, including probiotic Lactobacillus species. Numerous mechanisms for adhesion to mucus have been discovered in lactobacilli, including partially characterized mucus binding proteins. These mechanisms vary in importance with the in vitro models studied, which could significantly affect the perceived probiotic potential of the organisms. Understanding the nature of mucus-microbe interactions could be the key to elucidating the mechanisms of probiotic adhesion within the host.

Antimicrobial activity against Shigella sonnei and probiotic properties of wild lactobacilli from fermented food

Four lactobacilli strains (Lactobacillus paracasei subp. paracasei M5-L, Lactobacillus rhamnosus J10-L, Lactobacillus casei Q8-L and L. rhamnosus GG (LGG), were systematically assessed for the production of antimicrobial substances active towards Shigella sonnei, Escherichia coli and Salmonella typhimurium. Agar-well assay showed that the four lactobacilli strains displayed strong antibacterial activity towards S. sonnei. The nature of antimicrobial substances was also investigated and shown to be dependent on the production of organic acids, in particular the lactic acid. Time-kill assay showed that the viability of the S. sonnei was decreased by 2.7-3.6logCFU/ml after contact with CFCS (cell-free culture supernatants) of four lactobacilli for 2h, which confirmed the result of the agar-well assay. Further analysis of the organic acid composition in the CFCS revealed that the content of lactic acid range from 227 to 293mM. In addition, the aggregations properties, adherence properties and tolerance to simulated gastrointestinal conditions were also investigated in vitro tests. The result suggested that the M5-L, J10-L and Q8-L strains possess desirable antimicrobial activity towards S. sonnei and probiotic properties as LGG and could be potentially used as novel probiotic strains in the food industry.

LAB-Secretome: a genome-scale comparative analysis of the predicted extracellular and surface-associated proteins of Lactic Acid Bacteria

Background

In Lactic Acid Bacteria (LAB), the extracellular and surface-associated proteins can be involved in processes such as cell wall metabolism, degradation and uptake of nutrients, communication and binding to substrates or hosts. A genome-scale comparative study of these proteins (secretomes) can provide vast information towards the understanding of the molecular evolution, diversity, function and adaptation of LAB to their specific environmental niches.

Results

We have performed an extensive prediction and comparison of the secretomes from 26 sequenced LAB genomes. A new approach to detect homolog clusters of secretome proteins (LaCOGs) was designed by integrating protein subcellular location prediction and homology clustering methods. The initial clusters were further adjusted semi-manually based on multiple sequence alignments, domain compositions, pseudogene analysis and biological function of the proteins. Ubiquitous protein families were identified, as well as species-specific, strain-specific, and niche-specific LaCOGs. Comparative analysis of protein subfamilies has shown that the distribution and functional specificity of LaCOGs could be used to explain many niche-specific phenotypes.

A comprehensive and user-friendly database LAB-Secretome was constructed to store, visualize and update the extracellular proteins and LaCOGs http://www.cmbi.ru.nl/lab_secretome/. This database will be updated regularly when new bacterial genomes become available.

Conclusions

The LAB-Secretome database could be used to understand the evolution and adaptation of lactic acid bacteria to their environmental niches, to improve protein functional annotation and to serve as basis for targeted experimental studies.

Lactobacillus plantarum surface layer adhesive protein protects intestinal epithelial cells against tight junction injury induced by enteropathogenic Escherichia coli

Lactobacillus plantarum (LP) has previously been used for the treatment and prevention of intestinal disorders and disease. However, the role of the LP surface layer adhesive protein (SLAP) in inhibition of epithelial cell disruption is not fully understood. The aim of the present study was to investigate the protective effects of purified SLAP on Caco-2 cells infected with enteropathogenic Escherichia coli (EPEC). The role of ERK in LP-mediated inhibition of tight junction (TJ) injury was also evaluated in order to determine the molecular mechanisms underlying the protective effects of LP in epithelial cells. SLAP was extracted and purified from LP cells using a porcine stomach mucin-Sepharose 4B column. SLAP-mediated inhibition of bacterial adhesion was measured using a competition-based adhesion assay. Expression of TJ-associated proteins, maintenance of TJ structure, and levels of extracellular signal regulated kinase (ERK) and ERK phosphorylation were assessed in SLAP-treated cells by a combination of real-time PCR, western blotting, and immunofluorescence microscopy. Cell permeability was analyzed by measurement of trans-epithelial electrical resistance (TER) and dextran permeability. The effect of SLAP on levels of apoptosis in epithelial cells was assessed by flow cytometry. Results from these experiments revealed that treatment with SLAP decreased the level of adhesion of EPEC to Caco-2 cells. SLAP treatment also enhanced expression of TJ proteins at both the mRNA and protein levels and affected F-actin distribution. Although ERK levels remained unchanged, ERK phosphorylation was increased by SLAP treatment. Caco-2 cells treated with SLAP exhibited increased TER and decreased macromolecular permeability, which was accompanied by a decrease in the level of apoptosis. Together, these results suggest that LP-produced SLAP protects intestinal epithelial cells from EPEC-induced injury, likely through a mechanism involving ERK activation.

Extracellular proteins secreted by probiotic bacteria as mediators of effects that promote mucosa-bacteria interactions

During the last few years, a substantial body of scientific evidence has accumulated suggesting that certain surface-associated and extracellular components produced by probiotic bacteria could be responsible for some of their mechanisms of action. These bacterial components would be able to directly interact with the host mucosal cells; they include exopolysaccharides, bacteriocins, lipoteichoic acids and surface-associated and extracellular proteins. Extracellular proteins include proteins that are actively transported to the bacterial surroundings through the cytoplasmic membrane, as well as those that are simply shed from the bacterial surface. Compared to the other bacterial components, the interactive ability of extracellular proteins/peptides has been less extensively studied. In this review, current findings supporting an interaction between extracellular proteins/peptides produced by probiotic bacteria (strains of the genera Bifidobacterium, Lactobacillus and Escherichia) and host mucosal cells are discussed. Research needs and future trends are also considered.

Inhibition of Shigella sonnei adherence to HT-29 cells by lactobacilli from Chinese fermented food and preliminary characterization of S-layer protein involvement

In this study, seven lactobacilli with a high degree of antagonistic activity against three pathogens and good adherence to HT-29 cells were selected. The ability of these seven lactobacilli to inhibit adhesion of Shigella sonnei to intestinal mucosa was studied on cultured HT-29 cells. Lactobacilli were added simultaneously with, before or after S. sonnei to test for their effectiveness in exclusion, competition and displacement assays, respectively. Lactobacillus paracasei subp. paracasei M5-L, Lactobacillus rhamnosus J10-L and Lactobacillus casei Q8-L all exhibited significant inhibitory activity. In order to elucidate the inhibitory functions of S-layer proteins, the S-layer proteins were removed with 5 M LiCl from the M5-L, J10-L and Q8-L strains. Under such conditions, inhibition activity was decreased in all three strains, as revealed in exclusion, competition and displacement assays. SDS-PAGE analysis confirmed the presence of S-layer proteins with dominant bands of approximately 45 kDa. Further analysis of S-layer proteins revealed that the hydrophobic amino acids accounted for 40.5%, 41.5% and 43.8% of the total amino acid for the M5-L, J10-L and Q8-L strains, respectively. These findings suggest that the M5-L, J10-L and Q8-L strains possess the ability to inhibit S. sonnei adherence to HT-29 cells, and S-layer proteins are involved in this adhesion inhibition.

Expression of the Mucus Adhesion Gene Mub, Surface Layer Protein Slp and Adhesion-Like Factor EF-TU of Lactobacillus acidophilus ATCC 4356 Under Digestive Stress Conditions, as Monitored with Real-Time PCR

Expression of the mucus adhesion gene Mub, surface layer protein Slp and adhesion-like factor EF-Tu by Lactobacillus acidophilus ATCC 4356 grown in the presence of mucin, bile and pancreatin and at low pH was studied using real-time PCR. None of the genes were up-regulated under increasing concentrations of mucin, while Slp and EF-Tu were up-regulated in the presence of bile and pancreatin at normal concentrations (0.3%, w/v) and under stress conditions (1.0%, w/v).

Mechanisms of probiosis and prebiosis: considerations for enhanced functional foods

The technologies of metagenomics and metabolomics are broadening our knowledge of the roles the human gut microbiota play in health and disease. For many years now, probiotics and prebiotics have been included in foods for their health benefits; however, we have only recently begun to understand their modes of action. This review highlights recent advances in deciphering the mechanisms of probiosis and prebiosis, and describes how this knowledge could be transferred to select for enhancing functional foods targeting different populations. A special focus will be given to the addition of prebiotics and probiotics in functional foods for infants and seniors.

Genes and molecules of lactobacilli supporting probiotic action

Lactobacilli have been crucial for the production of fermented products for centuries. They are also members of the mutualistic microbiota present in the human gastrointestinal and urogenital tract. Recently, increasing attention has been given to their probiotic, health-promoting capacities. Many human intervention studies demonstrating health effects have been published. However, as not all studies resulted in positive outcomes, scientific interest arose regarding the precise mechanisms of action of probiotics. Many reported mechanistic studies have addressed mainly the host responses, with less attention being focused on the specificities of the bacterial partners, notwithstanding the completion of Lactobacillus genome sequencing projects, and increasing possibilities of genomics-based and dedicated mutant analyses. In this emerging and highly interdisciplinary field, microbiologists are facing the challenge of molecular characterization of probiotic traits. This review addresses the advances in the understanding of the probiotic-host interaction with a focus on the molecular microbiology of lactobacilli. Insight into the molecules and genes involved should contribute to a more judicious application of probiotic lactobacilli and to improved screening of novel potential probiotics.

Murein hydrolase activity in the surface layer of Lactobacillus acidophilus ATCC 4356

We describe a new enzymatic functionality for the surface layer (S-layer) of Lactobacillus acidophilus ATCC 4356, namely, an endopeptidase activity against the cell wall of Salmonella enterica serovar Newport, assayed via zymograms and identified by Western blotting. Based on amino acid sequence comparisons, the hydrolase activity was predicted to be located at the C terminus. Subsequent cloning and expression of the C-terminal domain in Bacillus subtilis resulted in the functional verification of the enzymatic activity.

Surface-bound proteins of Lactobacillus plantarum 423 that contribute to adhesion of Caco-2 cells and their role in competitive exclusion and displacement of Clostridium sporogenes and Enterococcus faecalis

Elongation factor Tu (EF-Tu), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and triosephosphate isomerase (TPI) are surface-bound proteins with a role in adhesion of Lactobacillus plantarum 423 to Caco-2 cells. Removal of surface-bound proteins from L. plantarum 423 (treated with 4M guanidine-HCl) reduced adhesion to Caco-2 cells by 40%. In a competitive exclusion experiment where all three strains were given an equal chance to adhere to Caco-2 cells, L. plantarum 423 prevented 71% of cells of Clostridium sporogenes LMG 13570 and 89% of cells of Enterococcus faecalis LMG 13566 from adhering. Cells of L. plantarum 423, from which surface-bound proteins were removed, prevented 49% of cells of C. sporogenes LMG 13570 and 70% of cells of E. faecalis LMG 13566 from adhering to Caco-2 cells, suggesting that factors other than surface-bound proteins are involved in adhesion. Colonization of L. plantarum 423 to Caco-2 cells prevented adhesion of 74% of cells of C. sporogenes LMG 13570 and 62% of cells of E. faecalis LMG 13566. Furthermore, L. plantarum 423 displaced 81% of cells of C. sporogenes LMG 13570 and 91% of cells of E. faecalis LMG 13566 from Caco-2 cells. L. plantarum 423 is a potential probiotic strain.

Proteomic investigation of the aggregation phenomenon in Lactobacillus crispatus

Aggregation process affects the ability of Lactobacillus crispatus, a probiotic, to survive into the gastro-intestinal environment and to adhere to the intestinal mucosa. To elucidate mechanisms underlying this process, a comparative proteomic study was carried out on a wild type strain M247 and its spontaneous isogenic mutant Mu5, which had lost the aggregative phenotype. Results highlighted an overall lower amount of enzymes involved in carbohydrate transport and metabolism in strain M247 compared to strain Mu5, suggesting a reduction in the general growth rate, probably caused by nutrient limitation in cell aggregates, coherently with the phenotypic traits of the strains. Moreover, the up-regulation of a putative elongation factor Tu in the wild type M247 strain could suggest a role of this particular protein in the adhesion mechanism of L. crispatus.

Adherence factors of Lactobacillus in the human gastrointestinal tract

Despite the increasing number of scientific reports describing adhesion of Lactobacillus to components of the human intestinal mucosa, information on the surface molecules mediating this adhesion and their corresponding receptors is fragmentary. This MiniReview compiles present knowledge of the genetically and functionally characterized Lactobacillus factors responsible for mediating adhesion to different components of the human gastrointestinal tract. In addition, for the proteins among these factors, the domain structure is discussed, and where appropriate the results of in silico analyses are reported.