Characterization of Lactobacillus coryniformis DSM 20001T surface protein Cpf mediating coaggregation with and aggregation among pathogens

Biosurfactant/s from Lactobacilli species: Properties, challenges and potential biomedical applications

Lactic acid bacteria are generally believed to have positive roles in maintaining good health and immune system in humans. A number of Lactobacilli spp. are known to produce important metabolites, among which biosurfactants in particular have shown antimicrobial activity against several pathogens in the intestinal tract and female urogenital tract partly through interfering with biofilm formation and adhesion to the epithelial cells surfaces. Around 46 reports are documented on biosurfactant production from Lactobacillus spp. of which six can be broadly classified as cell free biosurfactant and 40 as cell associated biosurfactants and only approximately 50% of those have reported on the structural composition which, in order of occurrence were mainly proteinaceous, glycolipidic, glycoproteins, or glycolipopeptides in nature. Due to the proteinaceous nature, most biosurfactant produced by strains of Lactobacillus are generally believed to be surlactin type with high potential toward impeding pathogens adherence. Researchers have recently focused on the anti-adhesive and antibiofilm properties of Lactobacilli-derived biosurfactants. This review briefly discusses the significance of Lactobacilli-derived biosurfactants and their potential applications in various fields. In addition, we highlight the exceptional prospects and challenges in fermentation economics of Lactobacillus spp.-derived biosurfactants' production processes.

Potentially probiotic and bioprotective lactic acid bacteria starter cultures antagonise the Listeria monocytogenes adhesion to HT29 colonocyte-like cells

The capability of five lactic acid bacteria (LAB) to counteract the adhesion of Listeria monocytogenes to the epithelial intestinal cell line HT29 was studied. The highest adhesion ability to HT29 was achieved by the intestinal strain Lactobacillus rhamnosus CTC1679, followed by the meat-derived strains Lactobacillus sakei CTC494 and Enterococcus faecium CTC8005. Surprisingly, the meat strains showed significantly better adhesion to HT29 than two faecal isolates of Lactobacillus casei and even significantly higher than the reference strain L. rhamnosus GG. Additionally, the anti-listerial, bacteriocin-producer starter culture L. sakei CTC494 was able to significantly reduce the adhesion of L. monocytogenes to HT29 in experiments of exclusion, competition and inhibition. The performance was better than the faecal isolate L. rhamnosus CTC1679. Our results reinforce the fact that the ability of LAB to interact with a host epithelium model, as well as to antagonise with foodborne pathogens, is a strain-specific characteristic. Additionally, it is underlined that this trait is not dependent on the origin of the bacterium, since some food LAB behave better than intestinal ones. Therefore, the search for novel strains in food niches is a suitable approach to find those with potential health benefits. These strains are likely pre-adapted to the food environment, which would make their inclusion in the formulation of probiotic foods more feasible.

The cell aggregating propensity of probiotic actinobacterial isolates: isolation and characterization of the aggregation inducing peptide pheromone

The auto-aggregating ability of a probiotic is a prerequisite for colonization and protection of the gastrointestinal tract, whereas co-aggregation provides a close interaction with pathogenic bacteria. Peptide pheromone mediated signaling has been studied in several systems. However, it has not yet been explored in prokaryotes, especially actinobacteria. Hence, in the present study, the diffusible aggregation promoting factor was purified from the culture supernatant of a potent actinobacterial probiont and characterized using 20 different actinobacterial cultures isolated from the gut region of chicken and goat. The results showed that the pheromone-like compound induces the aggregation propensity of treated isolates. The factor was found to be a heat stable, acidic pH resistant, low molecular weight peptide which enhances the biofilm forming ability of other actinobacterial isolates. The aggregation promoting factor represents a bacterial sex factor (pheromone) and its characterization confirms its usage in the probiotic formulation.

Prophage-mediated modulation of interaction of Streptococcus thermophilus J34 with human intestinal epithelial cells and its competition against human pathogens

The human intestinal microbiota plays an important role in human health. While adhesion to gastrointestinal mucosa is a prerequisite for colonisation, inhibition of adhesion is a property which may prevent or reduce infections by food borne pathogens. Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus represent the two lactic bacteria constituting the yoghurt culture. These starter cultures have been claimed to be probiotic. In our study we compared two S. thermophilus strains (i.e. lysogenic strain J34 and corresponding non-lysogenic [prophage-cured] strain J34-6), with respect to (1) their in vitro adhesion properties to HT29 cells and (2) their cell surface hydrophobicities. Effects of the two strains on inhibition of adhesion of the pathogens Listeria monocytogenes Scott A, Staphylococcus aureus 6732 and Salmonella enteritidis S489 were studied in vitro with HT29 cell cultures. Lysogenic strain J34 was shown to be considerably more effective than the non-lysogenic derivative strain J34-6.

Coaggregation between Rhodococcus and Acinetobacter strains isolated from the food industry

In this study, coaggregation interactions between Rhodococcus and Acinetobacter strains isolated from food-processing surfaces were characterized. Rhodococcus sp. strain MF3727 formed intrageneric coaggregates with Rhodococcus sp. strain MF3803 and intergeneric coaggregates with 2 strains of Acinetobacter calcoaceticus (MF3293, MF3627). Stronger coaggregation between A. calcoaceticus MF3727 and Rhodococcus sp. MF3293 was observed after growth in batch culture at 30 °C than at 20 °C, after growth in tryptic soy broth than in liquid R2A medium, and between cells in exponential and early stationary phases than cells in late stationary phase. The coaggregation ability of Rhodococcus sp. MF3727 was maintained even after heat and Proteinase K treatment, suggesting its ability to coaggregate was protein independent whereas the coaggregation determinants of the other strains involved proteinaceous cell-surface-associated polymers. Coaggregation was stable at pH 5–9. The mechanisms of coaggregation among Acinetobacter and Rhodococcus strains bare similarity to those displayed by coaggregating bacteria of oral and freshwater origin, with respect to binding between proteinaceous and nonproteinaceous determinants and the effect of environmental factors on coaggregation. Coaggregation may contribute to biofilm formation on industrial food surfaces, protecting bacteria against cleaning and disinfection.

AggLb Is the Largest Cell-Aggregation Factor from Lactobacillus paracasei Subsp. paracasei BGNJ1-64, Functions in Collagen Adhesion, and Pathogen Exclusion In Vitro

Eleven Lactobacillus strains with strong aggregation abilities were selected from a laboratory collection. In two of the strains, genes associated with aggregation capability were plasmid located and found to strongly correlate with collagen binding. The gene encoding the auto-aggregation-promoting protein (AggLb) of Lactobacillus paracasei subsp. paracasei BGNJ1-64 was cloned using a novel, wide-range-host shuttle cloning vector, pAZILSJ. The clone pALb35, containing a 11377-bp DNA fragment, was selected from the SacI plasmid library for its ability to provide carriers with the aggregation phenotype. The complete fragment was sequenced and four potential ORFs were detected, including the aggLb gene and three surrounding transposase genes. AggLb is the largest known cell-surface protein in lactobacilli, consisting of 2998 aa (318,611 Da). AggLb belongs to the collagen-binding superfamily and its C-terminal region contains 20 successive repeats that are identical even at the nucleotide level. Deletion of aggLb causes a loss of the capacity to form cell aggregates, whereas overexpression increases cellular aggregation, hydrophobicity and collagen-binding potential. PCR screening performed with three sets of primers based on the aggLb gene of BGNJ1-64 enabled detection of the same type of aggLb gene in five of eleven selected aggregation-positive Lactobacillus strains. Heterologous expression of aggLb confirmed the crucial role of the AggLb protein in cell aggregation and specific collagen binding, indicating that AggLb has a useful probiotic function in effective colonization of host tissue and prevention of pathogen colonization.

Extensive intra-phylotype diversity in lactobacilli and bifidobacteria from the honeybee gut

Background

In the honeybee Apis mellifera, the bacterial gut community is consistently colonized by eight distinct phylotypes of bacteria. Managed bee colonies are of considerable economic interest and it is therefore important to elucidate the diversity and role of this microbiota in the honeybee. In this study, we have sequenced the genomes of eleven strains of lactobacilli and bifidobacteria isolated from the honey crop of the honeybee A. mellifera.

Results

Single gene phylogenies confirmed that the isolated strains represent the diversity of lactobacilli and bifidobacteria in the gut, as previously identified by 16S rRNA gene sequencing. Core genome phylogenies of the lactobacilli and bifidobacteria further indicated extensive divergence between strains classified as the same phylotype. Phylotype-specific protein families included unique surface proteins. Within phylotypes, we found a remarkably high level of gene content diversity. Carbohydrate metabolism and transport functions contributed up to 45% of the accessory genes, with some genomes having a higher content of genes encoding phosphotransferase systems for the uptake of carbohydrates than any previously sequenced genome. These genes were often located in highly variable genomic segments that also contained genes for enzymes involved in the degradation and modification of sugar residues. Strain-specific gene clusters for the biosynthesis of exopolysaccharides were identified in two phylotypes. The dynamics of these segments contrasted with low recombination frequencies and conserved gene order structures for the core genes. Hits for CRISPR spacers were almost exclusively found within phylotypes, suggesting that the phylotypes are associated with distinct phage populations.

Conclusions

The honeybee gut microbiota has been described as consisting of a modest number of phylotypes; however, the genomes sequenced in the current study demonstrated a very high level of gene content diversity within all three described phylotypes of lactobacilli and bifidobacteria, particularly in terms of metabolic functions and surface structures, where many features were strain-specific. Together, these results indicate niche differentiation within phylotypes, suggesting that the honeybee gut microbiota is more complex than previously thought.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1476-6) contains supplementary material, which is available to authorized users.

The identification and functional characterization of WxL proteins from Enterococcus faecium reveal surface proteins involved in extracellular matrix interactions

The WxL domain recently has been identified as a novel cell wall binding domain found in numerous predicted proteins within multiple Gram-positive bacterial species. However, little is known about the function of proteins containing this novel domain. Here, we identify and characterize 6 Enterococcus faecium proteins containing the WxL domain which, by reverse transcription-PCR (RT-PCR) and genomic analyses, are located in three similarly organized operons, deemed WxL loci A, B, and C. Western blotting, electron microscopy, and enzyme-linked immunosorbent assays (ELISAs) determined that genes of WxL loci A and C encode antigenic, cell surface proteins exposed at higher levels in clinical isolates than in commensal isolates. Secondary structural analyses of locus A recombinant WxL domain-containing proteins found they are rich in β-sheet structure and disordered segments. Using Biacore analyses, we discovered that recombinant WxL proteins from locus A bind human extracellular matrix proteins, specifically type I collagen and fibronectin. Proteins encoded by locus A also were found to bind to each other, suggesting a novel cell surface complex. Furthermore, bile salt survival assays and animal models using a mutant from which all three WxL loci were deleted revealed the involvement of WxL operons in bile salt stress and endocarditis pathogenesis. In summary, these studies extend our understanding of proteins containing the WxL domain and their potential impact on colonization and virulence in E. faecium and possibly other Gram-positive bacterial species.

Impact of the exopolysaccharide layer on biofilms, adhesion and resistance to stress in Lactobacillus johnsonii FI9785

BACKGROUND

The bacterial cell surface is a crucial factor in cell-cell and cell-host interactions. Lactobacillus johnsonii FI9785 produces an exopolysaccharide (EPS) layer whose quantity and composition is altered in mutants that harbour genetic changes in their eps gene clusters. We have assessed the effect of changes in EPS production on cell surface characteristics that may affect the ability of L. johnsonii to colonise the poultry host and exclude pathogens.

RESULTS

Analysis of physicochemical cell surface characteristics reflected by Zeta potential and adhesion to hexadecane showed that an increase in EPS gave a less negative, more hydrophilic surface and reduced autoaggregation. Autoaggregation was significantly higher in mutants that have reduced EPS, indicating that EPS can mask surface structures responsible for cell-cell interactions. EPS also affected biofilm formation, but here the quantity of EPS produced was not the only determinant. A reduction in EPS production increased bacterial adhesion to chicken gut explants, but made the bacteria less able to survive some stresses.

CONCLUSIONS

This study showed that manipulation of EPS production in L. johnsonii FI9785 can affect properties which may improve its performance as a competitive exclusion agent, but that positive changes in adhesion may be compromised by a reduction in the ability to survive stress.

Isolation and Characterisation of Bacteriocin and Aggregation-Promoting Factor Production in Lactococcus lactis ssp. lactis BGBM50 Strain

Lactococcus lactis ssp. lactis BGBM50, a producer of lactococcin G and aggregation-promoting factor, was isolated from selected lactic acid bacteria taken from semi-hard cheese traditionally produced in the village Žanjic, Montenegro. Strain BGBM50 harbours a number of plasmids of different sizes. Plasmid curing experiments showed that genes for bacteriocin production are located on pBM140, a plasmid 140 kb in length. PCR analysis with primers specific for lactococcin Q and G genes gave fragment of the expected size. In addition, after plasmid curing of strain BGBM50, different derivatives with altered phenotypes were obtained, among them BGBM50-34 strain, which retained bacteriocin synthesis but had enhanced aggregation ability.

Unpasteurised commercial boza as a source of microbial diversity

Boza is a cereal-based fermented beverage widely consumed in many countries of the Balkans. The aim of this study was to investigate the microbiota of three Bulgarian boza samples through a combination of culture-dependent and -independent methods with the long-term objective of formulating a multi-strain starter culture specifically destined for the manufacture of new cereal-based drinks. The isolation campaign for lactic acid bacteria (LAB) allowed the identification of Lactobacillus parabuchneri, Lactobacillus fermentum, Lactobacillus coryniformis, Lactobacillus buchneri, Pediococcus parvulus and members of the Lactobacillus casei group. Concerning yeasts, the following isolates were identified: Pichia fermentans, Pichia norvegensis, Pichia guilliermondii (synonym Meyerozyma guilliermondii) and Torulaspora spp. A high intra-species diversity was revealed by Randomly Amplified Polymorphic DNA (RAPD) analysis. In parallel, microbial DNA was directly extracted from the three boza samples, and portions of the rrn operons were analysed through Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE). The molecular fingerprinting partially confirmed the results of culturing. Among LAB, the species Weissella confusa, Weissella oryzae, Leuconostoc citreum, Lactococcus lactis, Pediococcus parvulus and Pediococcus ethanolidurans were detected together with members of the Lb. casei group. Among the yeasts, the species P. fermentans, M. guilliermondii, Galactomyces geotrichum and Geotrichum fragrans were found. The overall results confirmed boza as having a rich and heterogeneous biodiversity both in terms of species and genetically diverse strains, thus encouraging its exploitation for the isolation and future technological characterisation of cultures to be selected for the manufacture of innovative cereal-based drinks.

Lactobacillus gasseri SBT2055 reduces infection by and colonization of Campylobacter jejuni

Campylobacter is a normal inhabitant of the chicken gut. Pathogenic infection with this organism in humans is accompanied by severe inflammation of the intestinal mucosal surface. The aim of this study was to evaluate the ability of Lactobacillus gasseri SBT2055 (LG2055) to inhibit the adhesion and invasion of Campylobacter jejuni in vitro and to suppress C. jejuni colonization of chicks in vivo. Pretreatment with LG2055 significantly reduced adhesion to and invasion of a human epithelial cell line, Intestine 407, by C. jejuni 81-176. Methanol (MeOH)-fixed LG2055 also reduced infection by C. jejuni 81-176. However, proteinase K (ProK)-treated LG2055 eliminated the inhibitory effects. Moreover, LG2055 co-aggregated with C. jejuni 81-176. ProK treatment prevented this co-aggregation, indicating that the co-aggregation phenotype mediated by the proteinaceous cell-surface components of LG2055 is important for reducing C. jejuni 81-176 adhesion and invasion. In an in vivo assay, oral doses of LG2055 were administered to chicks daily for 14 days after oral inoculation with C. jejuni 81-176. At 14 days post-inoculation, chicks treated with LG2055 had significantly reduced cecum colonization by C. jejuni. Reduction in the number of C. jejuni 81-176 cells adhering to and internalized by human epithelial cells demonstrated that LG2055 is an organism that effectively and competitively excludes C. jejuni 81-176. In addition, the results of the chick colonization assay suggest that treatment with LG2055 could be useful in suppressing C. jejuni colonization of the chicks at early growth stages.

Fimbriae and lipopolysaccharides are necessary for co-aggregation between Lactobacilli and Escherichia coli

Cells of Lactobacilli co-aggregated with Escherichia coli K-12 cells to form co-aggregates under mixed-culture conditions at 37 °C for 24 h. Co-aggregation was inhibited by sodium dodecyl sulfate but not by protease. E. coli deletion mutants of fimbriae formation and lipopolysaccharide (LPS) formation did not co-aggregate with Lactobacilli. These results showed that fimbriae and LPS are necessary for co-aggregation between Lactobacilli and E. coli.

In vitro and in vivo effects of beneficial vaginal lactobacilli on pathogens responsible for urogenital tract infections

The aim of this work was to evaluate the effects of beneficial human vaginal lactobacilli (Lb) on urogenital pathogens through in vitro and in vivo experiments. Co-aggregative and antimicrobial properties between five vaginal Lb strains and urogenital pathogens or potential pathogens (Streptococcus agalactiae, Staphylococcus aureus and Candida albicans strains) were assayed. Also, associative cultures of Lb strains and S. agalactiae were performed and bacterial growth, pH, lactic acid and hydrogen peroxide (H2O2) were determined at different times. Based on the results obtained, the in vivo studies were assayed in mice with Lactobacillus gasseri CRL 1509 or Lactobacillus salivarius CRL 1328 inoculated intravaginally (i.v.) and then challenged i.v. with S. agalactiae. Results were analysed by ANOVA (repeated measures and general linear models). Most of the Lb strains increased the percentage of aggregation of S. agalactiae strains. Only one strain (Lactobacillus reuteri CRL 1324) positively affected the aggregation of S. aureus and none increased the aggregation of C. albicans. The inhibition of the growth of S. agalactiae strains by production of organic acids by lactobacilli was evidenced. The Lb-S. agalactiae co-cultures showed a significant inhibition of the pathogen after 4 h and 8 h of incubation. Parallel increases in lactic acid and H2O2 levels were observed. However, in the experimental murine model, no significant differences were obtained in the number of streptococci recovered from the vaginal tract of control mice and those inoculated with Lb. In conclusion, vaginal Lb exhibited in vitro co-aggregative and antimicrobial effects on S. agalactiae strains, suggesting that they could be promising candidates for protection against S. agalactiae challenge. However, as these effects were not evidenced in the murine model used, further animal studies under different experimental conditions should be conducted to evaluate the preventive effect of Lb against challenge with S. agalactiae.

Biofilm formation of Salmonella serotypes in simulated meat processing environments and its relationship to cell characteristics

Salmonella attached to meat contact surfaces encountered in meat processing facilities may serve as a source of cross-contamination. In this study, the influence of serotypes and media on biofilm formation of Salmonella was investigated in a simulated meat processing environment, and the relationships between biofilm formation and cell characteristics were also determined. All six serotypes (Salmonella enterica serotype Heidelberg, Salmonella Derby, Salmonella Agona, Salmonella Indiana, Salmonella Infantis, and Salmonella Typhimurium) can readily form biofilms on stainless steel surfaces, and the amounts of biofilms were significantly influenced by the serotypes, incubation media, and incubation time used in this study. Significant differences in cell surface hydrophobicity, autoaggregation, motility, and growth kinetic parameters were observed between individual serotypes tested. Except for growth kinetic parameters, the cell characteristics were correlated with the ability of biofilm formation incubated in tryptic soy broth, whereas no correlation with biofilm formation incubated in meat thawing-loss broth (an actual meat substrate) was found. Salmonella grown in meat thawing-loss broth showed a "cloud-shaped" morphology in the mature biofilm, whereas when grown in tryptic soy broth it had a "reticulum-shaped" appearance. Our study provides some practical information to understand the process of biofilm formation on meat processing contact surfaces.

Probiotic potential and safety properties of Lactobacillus plantarum from Slovak Bryndza cheese

One hundred and twenty-five acid-resistant presumptive lactobacilli were isolated from Slovak Bryndza cheese and screened for their antimicrobial activity against eight bacterial pathogens using spot agar assay. Out of twenty-six Lactobacillus strains with strong inhibition activity, twenty were identified as Lactobacillus plantarum and six as Lactobacillus fermentum. The most active eleven L. plantarum isolates were further characterized in vitro for some probiotic and safety properties. Only three isolates K10, K21, and ZS07 showed the ability to grow over 50% in the presence of 0.3% bile. Strong deconjugation efficiency was determined for CK06 and K21. The highest β-galactosidase activity was shown in isolates ZS11, B01, CK06, and ZS07. Only three of the strains had the ability to produce tyramine: CK06, LM1, and ZS11. Strains K09, K21, ZS11, and ZS15 were susceptible to all tested antibiotics. Analysis of the results confirmed the L. plantarum isolates ZS07 and K21 as the most suitable for probiotic use, due to their desirable probiotic and safety characteristics.

An extracellular Serine/Threonine-rich protein from Lactobacillus plantarum NCIMB 8826 is a novel aggregation-promoting factor with affinity to mucin

Autoaggregation in lactic acid bacteria is directly related to the production of certain extracellular proteins, notably, aggregation-promoting factors (APFs). Production of aggregation-promoting factors confers beneficial traits to probiotic-producing strains, contributing to their fitness for the intestinal environment. Furthermore, coaggregation with pathogens has been proposed to be a beneficial mechanism in probiotic lactic acid bacteria. This mechanism would limit attachment of the pathogen to the gut mucosa, favoring its removal by the human immune system. In the present paper, we have characterized a novel aggregation-promoting factor in Lactobacillus plantarum. A mutant with a knockout of the D1 gene showed loss of its autoaggregative phenotype and a decreased ability to bind to mucin, indicating an adhesion role of this protein. In addition, heterologous production of the D1 protein or an internal fragment of the protein, characterized by its abundance in serine/threonine, strongly induced autoaggregation in Lactococcus lactis. This result strongly suggested that this internal fragment is responsible for the bioactivity of D1 as an APF. To our knowledge, this is the first report on a gene coding for an aggregation-promoting factor in Lb. plantarum.

Genomic analysis by deep sequencing of the probiotic Lactobacillus brevis KB290 harboring nine plasmids reveals genomic stability

We determined the complete genome sequence of Lactobacillus brevis KB290, a probiotic lactic acid bacterium isolated from a traditional Japanese fermented vegetable. The genome contained a 2,395,134-bp chromosome that housed 2,391 protein-coding genes and nine plasmids that together accounted for 191 protein-coding genes. KB290 contained no virulence factor genes, and several genes related to presumptive cell wall-associated polysaccharide biosynthesis and the stress response were present in L. brevis KB290 but not in the closely related L. brevis ATCC 367. Plasmid-curing experiments revealed that the presence of plasmid pKB290-1 was essential for the strain's gastrointestinal tract tolerance and tendency to aggregate. Using next-generation deep sequencing of current and 18-year-old stock strains to detect low frequency variants, we evaluated genome stability. Deep sequencing of four periodic KB290 culture stocks with more than 1,000-fold coverage revealed 3 mutation sites and 37 minority variation sites, indicating long-term stability and providing a useful method for assessing the stability of industrial bacteria at the nucleotide level.

Different roles for lactococcal aggregation factor and mucin binding protein in adhesion to gastrointestinal mucosa

Adhesion of bacteria to mucosal surfaces and epithelial cells is one of the key features for the selection of probiotics. In this study, we assessed the adhesion property of Lactococcus lactis subsp. lactis BGKP1 based on its strong autoaggregation phenotype and the presence of the mucin binding protein (MbpL). Genes involved in aggregation (aggL) and possible interaction with mucin (mbpL), present on the same plasmid pKP1, were previously separately cloned in the plasmid pAZIL. In vivo and in vitro experiments revealed potentially different physiological roles of these two proteins in the process of adherence to the intestine during the passage of the strain through the gastrointestinal tract. We correlated the in vitro and in vivo aggregation of the BGKP1-20 carrying plasmid with aggL to binding to the colonic mucus through nonspecific hydrophobic interactions. The expression of AggL on the bacterial cell surface significantly increased the hydrophobicity of the strain. On the other hand, the presence of AggL in the strain reduced its ability to adhere to the ileum. Moreover, MbpL protein showed an affinity to bind gastric type mucin proteins such as MUC5AC. This protein did not contribute to the binding of the strain to the ileal or colonic part of the intestine. Different potential functions of lactococcal AggL and MbpL proteins in the process of adhesion to the gastrointestinal tract are proposed.

Investigation of microorganisms involved in biosynthesis of the kefir grain

The purpose of this study was to understand the significance of each microorganism in grain formation by evaluating their microbial aggregation and cell surface properties during co-aggregation of LAB and yeasts together with an investigation of biofilm formation. Non-grain forming strains from viili were also evaluated as a comparison. Results indicated that the kefir grain strains, Lactobacillus kefiranofaciens and Saccharomyces turicensis possess strong auto-aggregation ability and that Lactobacillus kefiri shows significant biofilm formation properties. Significant co-aggregation was noted when S. turicensis and kefir LAB strains (Lb. kefiranofaciens and Lb. kefiri) were co-cultured. Most of the tested LAB strains are hydrophilic and had a negative charge on their cell surface. Only the kefir LAB strains, Lb. kefiranofaciens HL1 and Lb. kefiri HL2, possessed very high hydrophobicity and had a positive cell surface charge at pH 4.2. In contrast, the LAB and yeasts in viili did not show any significant self-aggregation or biofilm formation. Based on the above results, we propose that grain formation begins with the self-aggregation of Lb. kefiranofaciens and S. turicensis to form small granules. At this point, the biofilm producer, Lb. kefiri, then begins to attach to the surface of granules and co-aggregates with other organisms and components in the milk to form the grains. On sub-culturing, more organisms attach to the grains resulting in grain growth. When investigated by scanning electron microscopy, it was found that short-chain lactobacilli such as Lb. kefiri occupy the surface, while long-chain lactobacilli such as Lb. kefiranofaciens have aggregated towards the center of the kefir grains. These findings agree with the above hypothesis on the formation of grains. Taken together, this study demonstrates the importance of cell surface properties together with fermentation conditions to the formation of grains in kefir.

Role of extracellular transaldolase from Bifidobacterium bifidum in mucin adhesion and aggregation

The ability of bifidobacteria to establish in the intestine of mammals is among the main factors considered to be important for achieving probiotic effects. The role of surface molecules from Bifidobacterium bifidum taxon in mucin adhesion capability and the aggregation phenotype of this bacterial species was analyzed. Adhesion to the human intestinal cell line HT29 was determined for a collection of 12 B. bifidum strains. In four of them-B. bifidum LMG13195, DSM20456, DSM20239, and A8-the involvement of surface-exposed macromolecules in the aggregation phenomenon was determined. The aggregation of B. bifidum A8 and DSM20456 was abolished after treatment with proteinase K, this effect being more pronounced for the strain A8. Furthermore, a mucin binding assay of B. bifidum A8 surface proteins showed a high adhesive capability for its transaldolase (Tal). The localization of this enzyme on the surface of B. bifidum A8 was unequivocally demonstrated by immunogold electron microscopy experiments. The gene encoding Tal from B. bifidum A8 was expressed in Lactococcus lactis, and the protein was purified to homogeneity. The pure protein was able to restore the autoaggregation phenotype of proteinase K-treated B. bifidum A8 cells. A recombinant L. lactis strain, engineered to secrete Tal, displayed a mucin- binding level more than three times higher than the strain not producing the transaldolase. These findings suggest that Tal, when exposed on the cell surface of B. bifidum, could act as an important colonization factor favoring its establishment in the gut.

Invited review: Application of omics tools to understanding probiotic functionality

The human gut microbiota comprises autochthonous species that colonize and reside at high levels permanently and allochthonous species that originate from another source and are transient residents of the human gut. The interactions between bacteria and the human host can be classified as a continuum from symbiosis and commensalism (mutualism) to pathogenesis. Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. Recent advances in omics tools and sequencing techniques have furthered our understanding of probiotic functionality and the specific interactions between probiotics and their human hosts. Although it is known that not all probiotics use the same mechanisms to confer benefits on hosts, some specific mechanisms of action have been revealed through omic investigations. These include competitive exclusion, bacteriocin-mediated protection against intestinal pathogens, intimate interactions with mucin and the intestinal epithelium, and modulation of the immune system. The ability to examine fully sequenced and annotated genomes has greatly accelerated the application of genetic approaches to elucidate many important functional roles of probiotic microbes.

Identification and characterization of lactic acid bacteria isolated from mixed pasture of timothy and orchardgrass, and its badly preserved silage

In order to understand the relationship between lactic acid bacteria (LAB) species and silage fermentation, a total of 65 LAB strains isolated from mixed pasture of timothy (Phleum pratense L.) and orchardgrass (Dactylis glomerata L.), and its badly preserved silages were subjected to phenotypic and genetic analysis. According to these analyses, the isolates were divided into 13 groups, including Enterococcus gallinarum, Lactobacillus acidipiscis, L. coryniformis subsp. coryniformis, L. coryniformis subsp. torquens, L. curvatus, L. paraplantarum, L. plantarum subsp. argentoratensis, L. plantarum subsp. plantarum, L. sakei subsp. carnosus, Lactococcus garvieae, Lactococcus lactis subsp. cremoris, Leuconostoc pseudomesenteroides, Pediococcus acidilactici, Pediococcus pentosaceus, Weissella hellenica, Weissella paramesenteroides and Carnobacterium divergens. This is the first report to document that C. divergens, L. acidipiscis, L. sakei subsp. carnosus, L. garvieae, phenotypically novel L. lactis subsp. cremoris, E. gallinarum and W. hellenica are present in vegetative forage crops. L. plantarum group strains were most frequently isolated from the badly preserved silages. Some isolates showed a wide range of growth preferences for carbohydrate utilization, optimal growth pH and temperature in vitro, indicating that they have a high growth potential. These results are useful in understanding the diversity of LAB associated with decayed silage of timothy and orchardgrass.

In vitro evaluation of Lactobacillus gasseri strains of infant origin on adhesion and aggregation of specific pathogens

Numerous Lactobacillus species are members of the normal healthy human intestinal microbiota, and members of the Lactobacillus family predominate among the current marketed probiotic strains. Most of the current commercial probiotic strains have not been selected for specific applications but rather have been chosen based on their technological properties. Often the ability of such strains to temporarily colonize the gastrointestinal tract may be lacking, and the interactions with intestinal microbiota are few. Furthermore, the competitive exclusion properties of potential probiotic bacteria are strain specific and vary greatly. Thus, it is highly desirable that new candidate probiotic isolates originate from the healthy target population. In this study, seven newly isolated strains of Lactobacillus gasseri originating from feces of a healthy newborn child were evaluated for their ability to adhere to intestinal mucus, to autoaggregate and coaggregate with the model pathogens Cronobacter sakazakii (ATCC 29544) and Clostridium difficile (1296). All the bacterial strains, single or in combination, in viable and nonviable forms, were able to autoaggregate. The coaggregation with C. sakazakii or C. difficile was higher (P < 0.05) in nonviable than in the viable forms. Single L. gasseri strains showed similar adhesion abilities to intestinal colon mucus. The seven L. gasseri strains when combined were also able to significantly compete with, displace, and inhibit the adhesion of C. sakazakii and C. difficile in the mucus model. This study demonstrates that the studied L. gasseri strains fulfill the basic adhesion and aggregation properties for probiotics and could be considered for potential future use in children.

Microbiological and chemical characterisation of ting, a sorghum-based sourdough product from Botswana

Ting is a fermented sorghum product of Botswana which is used to prepare porridges of different consistencies. This study aimed to characterise ting with respect to fermentation microbiota and metabolite composition, and to develop starter cultures for ting fermentation. The pH values of 10 ting samples from Botswana ranged between 3.5 and 4.0 and cell counts ranged between 1.2×10(8) and 1.2×10(10)cfu/g lactic acid bacteria. Yeast cell counts were below 10(5)cfu/g in all samples and Enterobacteriaceae were less than 10 cfu/g. The microbiota of samples consisted of 2-4 dominant strains and strains were identified based on the sequence of their 16S rRNA genes as Lactobacillus reuteri, Lactobacillus fermentum, Lactobacillus harbinensis, Lactobacillus plantarum, Lactobacillus parabuchneri, Lactobacillus casei and Lactobacillus coryniformis. Binary strain combinations were employed as starter cultures to produce ting. Major fermentation products were lactate, acetate and ethanol, additionally, 1,2 propanediol and 1,3 propanediol were produced by some strains. All strains were capable of producing ting, which was accompanied by a decrease in pH from 6.3 to 4 within 8h. Traditionally processed ting requires 2 to 3 days to attain a pH below 4; the starter cultures thus reduced the fermentation time to 8h.

Lactobacilli antagonize the growth, motility, and adherence of Brachyspira pilosicoli: a potential intervention against avian intestinal spirochetosis

Avian intestinal spirochetosis (AIS) results from the colonization of the ceca and colorectum of poultry by pathogenic Brachyspira species. The number of cases of AIS has increased since the 2006 European Union ban on the use of antibiotic growth promoters, which, together with emerging antimicrobial resistance in Brachyspira, has driven renewed interest in alternative intervention strategies. Probiotics have been reported as protecting livestock against infection with common enteric pathogens, and here we investigate which aspects of the biology of Brachyspira they antagonize in order to identify possible interventions against AIS. The cell-free supernatants (CFS) of two Lactobacillus strains, Lactobacillus reuteri LM1 and Lactobacillus salivarius LM2, suppressed the growth of Brachyspira pilosicoli B2904 in a pH-dependent manner. In in vitro adherence and invasion assays with HT29-16E three-dimensional (3D) cells and in a novel avian cecal in vitro organ culture (IVOC) model, the adherence and invasion of B. pilosicoli in epithelial cells were reduced significantly by the presence of lactobacilli (P < 0.001). In addition, live and heat-inactivated lactobacilli inhibited the motility of B. pilosicoli, and electron microscopic observations indicated that contact between the lactobacilli and Brachyspira was crucial in inhibiting both adherence and motility. These data suggest that motility is essential for B. pilosicoli to adhere to and invade the gut epithelium and that any interference of motility may be a useful tool for the development of control strategies.

Lactic acid bacteria isolated from young calves--characterization and potential as probiotics

Lactic acid bacteria (LAB) are widely used as probiotics in humans and animals to restore the ecological balance of different mucosa. They help in the physiological functions of newborn calves that are susceptible to a variety of syndromes. The criteria for the selection of strains for the design of probiotic products are not available. Based in the host-specificity of the indigenous microbiota, 96 LAB isolates from faeces and oral cavity of calves were obtained. The surface properties were screened showing a small number of highly hydrophobic or autoagglutinating isolates. Also, a group produced H(2)O(2) and were able to inhibit pathogens, and two strains were bacteriocin-producers. Some grew at very low pH and high bile concentrations. The strains sharing some of the specific properties evaluated were identified genetically, assayed their compatibility and exopolysaccharide production. The results allow going further in the establishment of criteria to select strains to be included in a multi-strain-probiotic-product to be further assayed in animals.

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.

Functional roles of aggregation-promoting-like factor in stress tolerance and adherence of Lactobacillus acidophilus NCFM

Aggregation-promoting factors (Apf) are secreted proteins that have been associated with a diverse number of functional roles in lactobacilli, including self-aggregation, the bridging of conjugal pairs, coaggregation with other commensal or pathogenic bacteria, and maintenance of cell shape. In silico genome analysis of Lactobacillus acidophilus NCFM identified LBA0493 as a 696-bp apf gene that encodes a putative 21-kDa Apf protein. Transcriptional studies of NCFM during growth in milk showed apf to be one of the most highly upregulated genes in the genome. In the present study, reverse transcriptase-quantitative PCR (RT-QPCR) analysis revealed that the apf gene was highly induced during the stationary phase compared to that during the logarithmic phase. To investigate the functional role of Apf in NCFM, an Delta apf deletion mutant was constructed. The resulting Delta apf mutant, NCK2033, did not show a significant difference in cell morphology or growth compared to that of the NCFMDelta upp reference strain, NCK1909. The autoaggregation phenotype of NCK2033 in planktonic culture was unaffected. Additional phenotypic assays revealed that NCK2033 was more susceptible to treatments with oxgall bile and sodium dodecyl sulfate (SDS). Survival rates of NCK2033 decreased when stationary-phase cells were exposed to simulated small-intestinal and gastric juices. Furthermore, NCK2033 in the stationary phase showed a reduction of in vitro adherence to Caco-2 intestinal epithelial cells, mucin glycoproteins, and fibronectin. The data suggest that the Apf-like proteins may contribute to the survival of L. acidophilus during transit through the digestive tract and, potentially, participate in the interactions with the host intestinal mucosa.

Interaction of probiotics and pathogens--benefits to human health?

The probiotic terminology has matured over the years and currently a unified definition has been formed. Lactic acid bacteria (LAB) and bifidobacteria have been reported to remove heavy metals, cyanotoxins and mycotoxins from aqueous solutions. The binding processes appear to be species and strain specific. The most efficient microbial species and strains in the removal of these compounds vary between components tested. However, it is of interest to note that most strains characterized until now do not bind positive components or nutrients in the diet. This has significant implications to future detoxification biotechnology development. In a similar manner, lactic acid bacteria and bifidobacteria interact directly with viruses and pathogens in food and water as well as toxin producing microbes and some toxins. This review updates information and aims to characterize these interactions in association. The target is to understand probiotic health effects and to relate the mechanisms and actions to future potential of specific probiotic bacteria on decontamination of foods and water, and diets. The same aim is targeted in characterizing the role of probiotics in inactivating pathogens and viruses of health importance to facilitate the establishment of novel means of disease risk reduction related health benefits.

Isolation and functional characterization of a biosurfactant produced by Lactobacillus paracasei

In this study, the crude biosurfactant produced by a Lactobacillus paracasei strain isolated in a Portuguese dairy industry was characterized. The minimum surface tension (41.8mN/m) and the critical micelle concentration (2.5mg/ml) obtained were found to be similar to the values previously reported for biosurfactants isolated from other lactobacilli. The biosurfactant was found to be stable to pH changes over a range from 6 to 10, being more effective at pH 7, and showed no loss of surface activity after incubation at 60 degrees C for 120h. Although the biosurfactant chemical composition has not been determined yet, a fraction was isolated through acidic precipitation, which exhibited higher surface activity as compared with the crude biosurfactant. Furthermore, this isolated biosurfactant showed antimicrobial and anti-adhesive activities against several pathogenic microorganisms. In addition, L. paracasei exhibited a strong autoaggregating phenotype, which was maintained after washing and resuspending the cells in PBS, meaning that this attribute must be related to cell surface components and not to excreted factors. The autoaggregation ability exhibited by this strain, together with the antimicrobial and anti-adhesive properties observed for this biosurfactant opens the possibility for its use as an effective probiotic strain.

In vitro antagonistic activities of Lactobacillus spp. against Brachyspira hyodysenteriae and Brachyspira pilosicoli

The sensitivity of Brachyspira hyodysenteriae and Brachyspira pilosicoli, respectively the causative agents of Swine Dysentery and Porcine Intestinal Spirochaetosis to two probiotic Lactobacillus strains, L. rhamnosus CNCM-I-3698 and L. farciminis CNCM-I-3699 was studied through viability, motility and coaggregation assays. The cell-free supernatant of these lactobacilli contains lactic acid, that is stressful for Brachyspira (leading to the formation of spherical bodies), and lethal. It was demonstrated for the first time the in vitro coaggregation properties of two probiotic Lactobacillus strains (active or heat-treated) with two pathogenic strains of Brachyspira, leading to (1) trapping of spirochaetal cells in a physical network as demonstrated by SEM; (2) inhibition of the motility of Brachyspira. Such in vitro studies should encourage in vivo studies in animal model to evaluate the potential of the use of probiotic lactobacilli through a feeding strategy for the prevention of B. hyodysenteriae and B. pilosicoli.

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.

Bacterial populations in the vaginas of healthy adolescent women

Given that the microbiota of the healthy vagina plays an important role in the maintenance of health, it follows that an understanding of its composition and development may offer insights into the etiology and prevention of disease. In contrast to previous studies, this study exclusively investigated the structure and composition of adolescent vaginal bacterial communities. In this report, the vaginal bacterial communities of 90 menarcheal adolescents, ages 13-18y, were characterized using terminal restriction fragment length polymorphisms (T-RFLP) of 16S rRNA genes. Further characterization involved cluster analysis of the T-RFLP data to identify the number of different kinds of microbial communities found among the adolescents sampled, and phylogenetic analysis of 16S rRNA gene sequences cloned from samples representative of each cluster. We report the identification of four major clusters that accounted for 96.7% of the cohort. In general, these clusters could be divided into those dominated by Lactobacillus spp. and those dominated by a variety of lactic acid producing, anaerobic bacterial types such as Atopobium vaginae and Streptococcus spp. The compositional and structural similarity of the vaginal microbiota of menarcheal adolescents and adults suggests that the vaginal microbiota does not change significantly after the onset of menarche.

Some factors affecting the autoaggregation ability of vaginal lactobacilli isolated from Turkish women

In this work, autoaggregation and factors involved in the autoaggregation ability of vaginal lactobacilli were studied. The autoaggregation ability of 28 lactobacilli strains was positive. The effects of various factors on autoaggregation were also evaluated. Lactobacillus jensenii A1, L. salivarius I1, and L. cellobiosus I3 showed higher autoaggregation in acidic conditions and lower autoaggregation in hot (70 and 85oC) conditions. The L. salivarius I1 strain, which exhibited high autoaggregation activity, also showed good autoaggregation in pepsin, lipase, and sodium periodate, as well as under conditions of sonication and heat. The results of this study suggest that lactobacilli showing high autoaggregation may constitute an important host defense mechanism against infections as a probiotic.

Specific probiotic strains and their combinations counteract adhesion of Enterobacter sakazakii to intestinal mucus

Enterobacter sakazakii is an opportunistic pathogen and an occasional contaminant in powdered infant formula. Interaction between specific probiotics and E. sakazakii may reduce the risk of infection. The aim of this study was to characterize in vitro the ability of probiotics (alone and in combinations) to inhibit, compete with and displace the adhesion of E. sakazakii to immobilized human mucus and to assess their capacity to aggregate with pathogen. Specific probiotic strains have proved to aggregate E. sakazakii cells and, through competitive exclusion, inhibition and displacement of the adhered pathogen, were able to inhibit E. sakazakii action on intestinal mucus. The ability to inhibit and to displace adhered pathogen depended on both the probiotic and the pathogen, suggesting that several complementary mechanisms are involved in the processes. We suggest that the selection of specific probiotic strains and their combinations may be a useful means of counteracting E. sakazakii contamination in infant formula and thus to reduce the risk of emerging infection. This approach may also allow the development of new probiotic combinations to counteract the risks associated with other pathogens by improving the intestinal barrier against pathogens.

Direct selection and phage display of a Gram-positive secretome

A phage display system for direct selection, identification, expression and purification of bacterial secretome proteins has been developed.

Surface, secreted and transmembrane protein-encoding open reading frames, collectively the secretome, can be identified in bacterial genome sequences using bioinformatics. However, functional analysis of translated secretomes is possible only if many secretome proteins are expressed and purified individually. We have now developed and applied a phage display system for direct selection, identification, expression and purification of bacterial secretome proteins.

Measurement of aggregation properties between probiotics and pathogens: In vitro evaluation of different methods

Aggregation properties of probiotics with pathogens are of importance for both food preservation and therapeutic impact of food on intestinal microbiota. We assessed spectrophotometry, fluorescence and radioactivity techniques to characterize and quantify co-aggregation. Probiotic strains tested showed co-aggregation abilities, which were strain-specific and dependent on time and incubation conditions. Co-aggregation may be useful for preliminary screening in order to identify potentially probiotic strains suitable for food, human or animal use.

Molecular Characterization of a Novel Bacteriocin and an Unusually Large Aggregation Factor of Lactobacillus paracasei subsp. paracasei BGSJ2-8, a Natural Isolate from Homemade Cheese

Screening the collection of natural isolates from semi-hard homemade cheese resulted in isolation and characterization of strain Lactobacillus paracasei subsp. paracasei BGSJ2-8. The strain BGSJ2-8 harbors several important phenotypes, such as bacteriocin production, aggregation phenomenon, and production of proteinase. Bacteriocin SJ was purified by three-step chromatography. Mass spectrometry established molecular mass of the active peptide at 5372 Da. The auto-aggregation phenotype of wild-type (WT) strain was mediated by secreted aggregation-promoting factor (protein of molecular mass > 200 kDa), probably acting in cooperation with other cell surface protein(s). Comparative study of WT and its spontaneous nonaggregating derivative revealed that aggregation factor was responsible for the observed differences in the bacteriocin and proteinase activities. Bacteriocin SJ activity and resistance to different stresses were higher in the presence of aggregating factor. In contrast, proteinase activity was stronger in the nonaggregating derivative.