Culture conditions determine the balance between two different exopolysaccharides produced by Lactobacillus pentosus LPS26

Lactobacillus pentosus LPS26, isolated from a natural fermentation of green olives, produces a capsular polymer constituted of two exopolysaccharides (EPS): EPS A, a high-molecular-weight (high-Mw) polysaccharide (1.9x10(6) Da) composed of glucose and rhamnose (3:1), and EPS B, a low-Mw polysaccharide (3.3x10(4) Da) composed of glucose and mannose (3:1). Fermentation experiments in a chemically semidefined medium with different carbon sources (glucose, fructose, mannitol, and lactose) showed that all of them except fructose supported EPS A production rather than EPS B production. The influence of temperature and pH was further analyzed. As the temperature dropped, increased synthesis of both EPS was detected. The control of pH especially enhanced EPS B production. With regard to this, the maximum total EPS production (514 mg liter-1) was achieved at a suboptimal growth temperature (20 degrees C) and pH 6.0. Continuous cultures showed that EPS A, synthesized mainly at low dilution rates, is clearly dependent on the growth rate, whereas EPS B synthesis was hardly affected. EPS production was also detected in supplemented skimmed milk, but no increase on the viscosity of the fermented milk was recorded. This could be linked to the high proportion of the low-Mw polysaccharide produced in these conditions in contrast to that observed in culture media. Overall, the present study shows that culture conditions have a clear impact on the type and concentration of EPS produced by strain LPS26, and consequently, these conditions should be carefully selected for optimization and application studies. Finally, it should be noted that this is, to our knowledge, the first report on EPS production by L. pentosus.     

Structure of the high-molecular weight exopolysaccharide isolated from Lactobacillus pentosus LPS26

The strain Lactobacillus pentosus LPS26 produces a capsular polymer composed of a high- (2.0 × 10⁶ Da) (EPS A) and a low-molecular mass (2.4 × 10⁴ Da) (EPS B) polysaccharide when grown on semi-defined medium containing glucose as the carbon source. The structure of EPS A and its deacetylated form has been determined by monosaccharide and methylation analysis as well as by 1D/2D NMR studies (¹H and ¹³C). We conclude that EPS A is a charged heteropolymer, with a composition of d-glucose, d-glucuronic acid and l-rhamnose in a molar ratio 1:2:2. The repeating unit is a pentasaccharide with two O-acetyl groups at O-4 of the 3-substituted α-d-glucuronic acid and at O-2 of the 3-substituted β-l-rhamnose, respectively.→4)-α-d-Glcp-(1→3)-α-d-GlcpA4Ac-(1→3)-α-l-Rhap-(1→4)-α-d-GlcpA-(1→3)-β-l-Rhap2Ac-(1→This unbranched structure is not common in EPSs produced by Lactobacilli. Moreover, the presence of acetyl groups in the structure is an unusual feature which has only been reported in L. sake 0-1 [Robijn et al. Carbohydr. Res., 1995, 276, 117-136].     

Structure and Biosynthesis of Two Exopolysaccharides Produced by Lactobacillus johnsonii FI9785

Exopolysaccharides were isolated and purified from Lactobacillus johnsonii FI9785, which has previously been shown to act as a competitive exclusion agent to control Clostridium perfringens in poultry. Structural analysis by NMR spectroscopy revealed that L. johnsonii FI9785 can produce two types of exopolysaccharide: EPS-1 is a branched dextran with the unusual feature that every backbone residue is substituted with a 2-linked glucose unit, and EPS-2 was shown to have a repeating unit with the following structure: -6)-α-Glcp-(1–3)-β-Glcp-(1–5)-β-Galf-(1–6)-α-Glcp-(1–4)-β-Galp-(1–4)-β-Glcp-(1-. Sites on both polysaccharides were partially occupied by substituent groups: 1-phosphoglycerol and O-acetyl groups in EPS-1 and a single O-acetyl group in EPS-2. Analysis of a deletion mutant (ΔepsE) lacking the putative priming glycosyltransferase gene located within a predicted eps gene cluster revealed that the mutant could produce EPS-1 but not EPS-2, indicating that epsE is essential for the biosynthesis of EPS-2. Atomic force microscopy confirmed the localization of galactose residues on the exterior of wild type cells and their absence in the ΔepsE mutant. EPS2 was found to adopt a random coil structural conformation. Deletion of the entire 14-kb eps cluster resulted in an acapsular mutant phenotype that was not able to produce either EPS-2 or EPS-1. Alterations in the cell surface properties of the EPS-specific mutants were demonstrated by differences in binding of an anti-wild type L. johnsonii antibody. These findings provide insights into the biosynthesis and structures of novel exopolysaccharides produced by L. johnsonii FI9785, which are likely to play an important role in biofilm formation, protection against harsh environment of the gut, and colonization of the host.     

戊糖乳杆菌31-1菌株产细菌素发酵条件优化

对戊糖乳杆菌31-1产细菌素的条件进行了优化,分别研究了培养温度,培养基起始pH值,培养基碳源、氮源,刺激因子等因素对细菌素产量的影响。组合因素优化结果得到最佳培养基与培养条件为：乳糖30g、胰胨15g、豆胨20g、牛肉膏30g、蛋白胨20g、吐温801mL、磷酸氢二钾2g、乙酸钠5g、柠檬酸铵2g、硫酸镁0．58g、硫酸锰0．25g,蒸馏水定容至1000mL,30℃培养24h,培养起始pH为6．5。在此条件下培养细菌素效价可达到640AU／mL,与起始培养基相比细菌素产量提高了8倍。     

Acetobacter xylinum NUST4合成细菌纤维素发酵条件的优化

采用均匀设计法优化了Acetobacter xylinumNUST4的基础培养基,向其中添加了Mg2 、Fe2 、对氨基苯甲酸、烟酸、生物素、乙醇,优化后的发酵培养基组成为:葡萄糖24g,蔗糖22g,蛋白胨16g,醋酸2.4mL,磷酸氢二钠3.5g,磷酸二氢钾1g,硫酸镁6g,硫酸亚铁0.015g,烟酸0.003g,生物素0.02g和乙醇20mL,纤维素产量达9.87g,定容至1L,比由S-H培养基发酵合成的纤维素产量(仅0.74g.L-1)提高了12倍。     

Culture Conditions Affect the Molecular Weight Properties of Hyaluronic Acid Produced by Streptococcus zooepidemicus

The effect of five culture variables on the molecular weight properties of hyaluronic acid (HA) produced by Streptococcus zooepidemicus was studied in batch culture with a complex medium containing glucose and 10 g of yeast extract per liter. Neither the culture pH (pH 6.3 to 8.0) nor the agitation speed (300 to 1,000 rpm) affected the weight-average molecular weight (M(infw)) of HA under anaerobic conditions at 37(deg)C when 20 g of glucose per liter was used initially. M(infw) was in the narrow range of 1.5 x 10(sup6) to 2.3 x 10(sup6), and polydispersity (P) was between 1.8 and 2.5. When S. zooepidemicus was grown at lower temperatures or with aeration, higher-molecular-weight polymer and increased yields were observed. The polydispersity, however, remained unaffected. Anaerobically, the mean M(infw) (based on three samples taken within 4 h of glucose exhaustion) was (2.40 (plusmn) 0.10) x 10(sup6) and (1.90 (plusmn) 0.05) x 10(sup6) at 32 and 40(deg)C respectively. Aeration of the culture at 1 vol/vol/min produced HA with mean M(infw) of (2.65 (plusmn) 0.05) x 10(sup6) compared with (2.10 (plusmn) 0.10) x 10(sup6) under equivalent anaerobic conditions. The initial glucose concentration had the most pronounced effect on polymer characteristics. Increasing this concentration from 20 to 40 g/liter produced HA with mean M(infw) of (3.1 (plusmn) 0.1) x 10(sup6) at 1-vol/vol/min aeration. The molecular weight of HA also exhibited time dependency, with smaller chains (M(infw), ca. 2.5 x 10(sup6)) detected early in the culture time course, rising to a maximum (M(infw), 3.2 x 10(sup6)) in the late exponential phase of growth. The mean polydispersity was also greater (2.7 (plusmn) 0.1) under these conditions. Replicate experiments performed under conditions resulting in the lowest (40(deg)C, anaerobic) and highest (40 g of glucose per liter, 1-vol/vol/min aeration)-M(infw) polymer demonstrated excellent experimental reproducibility.     

Interactions between Bifidobacterium and Bacteroides Species in Cofermentations Are Affected by Carbon Sources,Including Exopolysaccharides Produced by Bifidobacteria

Cocultures of strains from two Bifidobacterium and two Bacteroides species were performed with exopolysaccharides (EPS) previously purified from bifidobacteria, with inulin, or with glucose as the carbon source. Bifidobacterium longum NB667 and Bifidobacterium breve IPLA20004 grew in glucose but showed poor or no growth in complex carbohydrates (inulin, EPS E44, and EPS R1), whereas Bacteroides grew well in the four carbon sources tested. In the presence of glucose, the growth of Bacteroides thetaiotaomicron DSM-2079 was inhibited by B. breve, whereas it remained unaffected in the presence of B. longum. Ba. fragilis DSM-2151 contributed to a greater survival of B. longum, promoting changes in the synthesis of short-chain fatty acids (SCFA) and organic acids in coculture with respect to monocultures. In complex carbohydrates, cocultures of bifidobacterium strains with Ba. thetaiotaomicron did not modify the behavior of Bacteroides nor improve the poor growth of bifidobacteria. The metabolic activity of Ba. fragilis in coculture with bifidobacteria was not affected by EPS, but greater survival of bifidobacteria at late stages of incubation occurred in cocultures than in monocultures, leading to a higher production of acetic acid than in monocultures. Therefore, cocultures of Bifidobacterium and Bacteroides can behave differently against fermentable carbohydrates as a function of the specific characteristics of the strains from each species. These results stress the importance of considering specific species and strain interactions and not simply higher taxonomic divisions in the relationship among intestinal microbial populations and their different responses to probiotics and prebiotics.     

Exopolysaccharides Produced by Streptococcus mutans Glucosyltransferases Modulate the Establishment of Microcolonies within Multispecies Biofilms

Streptococcus mutans is a key contributor to the formation of the extracellular polysaccharide (EPS) matrix in dental biofilms. The exopolysaccharides, which are mostly glucans synthesized by streptococcal glucosyltransferases (Gtfs), provide binding sites that promote accumulation of microorganisms on the tooth surface and further establishment of pathogenic biofilms. This study explored (i) the role of S. mutans Gtfs in the development of the EPS matrix and microcolonies in biofilms, (ii) the influence of exopolysaccharides on formation of microcolonies, and (iii) establishment of S. mutans in a multispecies biofilm in vitro using a novel fluorescence labeling technique. Our data show that the ability of S. mutans strains defective in the gtfB gene or the gtfB and gtfC genes to form microcolonies on saliva-coated hydroxyapatite surfaces was markedly disrupted. However, deletion of both gtfB (associated with insoluble glucan synthesis) and gtfC (associated with insoluble and soluble glucan synthesis) is required for the maximum reduction in EPS matrix and biofilm formation. S. mutans grown with sucrose in the presence of Streptococcus oralis and Actinomyces naeslundii steadily formed exopolysaccharides, which allowed the initial clustering of bacterial cells and further development into highly structured microcolonies. Concomitantly, S. mutans became the major species in the mature biofilm. Neither the EPS matrix nor microcolonies were formed in the presence of glucose in the multispecies biofilm. Our data show that GtfB and GtfC are essential for establishment of the EPS matrix, but GtfB appears to be responsible for formation of microcolonies by S. mutans; these Gtf-mediated processes may enhance the competitiveness of S. mutans in the multispecies environment in biofilms on tooth surfaces.Oral diseases related to dental biofilms afflict the majority of the world''s population, and dental caries is still the single most prevalent and costly oral infectious disease (12, 32). Dental caries results from the interaction of specific bacteria with constituents of the diet within a biofilm formed on the tooth surface known as plaque (5, 36). Streptococcus mutans is a key contributor to the formation of biofilms associated with dental caries disease, although other microorganisms may also be involved (3); S. mutans (i) effectively utilizes dietary sucrose (and possibly starch) to rapidly synthesize exopolysaccharides (EPS) using glucosyltransferases and a fructosyltransferase that adsorb to surfaces, (ii) adheres tenaciously to glucan-coated surfaces, and (iii) is acidogenic and acid tolerant (5, 30).In general, biofilms develop after initial attachment of microbes to a surface, followed by formation of highly structured cell clusters (or microcolonies) and further development and stabilization of the microcolonies, which are in a complex extracellular matrix (6, 49). The majority of biofilm matrices contain exopolysaccharides, and dental biofilms are no exception; up to 40% of the dry weight of dental plaque is composed of polysaccharides (depending on the type of carbohydrate consumption and the time of plaque collection), which are mostly glucans synthesized by microbial glucosyltransferases (Gtfs) (for a review, see reference 36). S. mutans plays a major role in the development and establishment of the EPS matrix in dental biofilms. This bacterium produces at least three Gtfs, which are products of the gtfB, gtfC, and gtfD genes; GtfB synthesizes mostly insoluble glucans containing elevated amounts of α-1,3-linked glucose, GtfC synthesizes a mixture of insoluble and soluble glucans (rich in α-1,6-linked glucose), and GtfD synthesizes predominantly soluble glucans (for reviews, see references 30 and 36). The Gtfs secreted by S. mutans bind avidly to the pellicle formed on the tooth surface and to bacterial surfaces and are enzymatically active; when they are exposed to sucrose, glucans are formed in situ within minutes (17, 33, 38, 40, 46). It is noteworthy that most nonstreptococcal oral bacteria (e.g., Actinomyces and Veillonella spp.) do not produce glucans unless Gtfs are adsorbed on their surfaces (33, 46). The glucans synthesized in situ provide binding sites for colonization and accumulation of S. mutans on the apatitic surface and for binding to each other through interactions with several membrane-associated glucan-binding proteins and surface glucans (8, 39, 47). The exopolymers also contribute to the bulk and physical integrity and stability of the biofilm matrix (for a review, see reference 36). The glucan-mediated processes promote tight adherence and coherence of bacterial cells bound to each other and to the apatitic surface, which leads to the formation of microcolonies by S. mutans and thereby modulates the initial steps of cariogenic biofilm development.When dietary sucrose is consumed frequently, S. mutans, as a member of the oral biofilm community, continues to synthesize polysaccharides and metabolize this sugar to form organic acids. The elevated amounts of EPS, which may involve upregulation of gtf genes in response to pH and carbohydrate availability (29), increase the virulence of the biofilms (42, 51). In addition, the ability of S. mutans to utilize some extra- and intracellular polysaccharides as short-term storage compounds provides an additional ecological benefit and simultaneously increases the amount of acid produced and the extent of acidification within the biofilm (5, 7). The persistence of this aciduric environment leads to selection and dominance of highly acid-tolerant (and acidogenic) organisms, such as S. mutans (32, 37); the low-pH environment in the biofilm matrix results in dissolution of enamel, thus initiating the pathogenesis of dental caries (32, 36).Recently, we have shown that EPS produced by S. mutans Gtfs modulate the initial formation, sequence of assembly, and structural organization of microcolonies by this bacterium on apatitic surfaces (50). However, it was unclear which of the Gtf enzymes were associated with these processes. Furthermore, the polysaccharides may also modulate the formation of microcolonies by complex ecological interactions in a multispecies system. In this study, we investigated (i) the role of each of the S. mutans gtf genes in EPS matrix and microcolony development on a saliva-coated hydroxyapatite (sHA) surface and (ii) the influence of exopolysaccharides on establishment of microcolonies at distinct developmental phases during formation of biofilms by S. mutans in the presence of Streptococcus oralis and Actinomyces naeslundii.(This study was presented at 5th ASM Conference on Biofilms, Cancun, Mexico, 15 to 19 November 2009.)     

Biosynthesis of Indolocarbazole and Goadsporin,Two Different Heterocyclic Antibiotics Produced by Actinomycetes

The biosynthesis of staurosporine, rebeccamycin, and goadsporin, which are produced by actinomycetes and contain characteristic heterocyclic rings, was characterized by genetic methods. Staurosporine and rebeccamycin contain an indolocarbazole ring synthesized from two molecules of tryptophan, with indolepyruvic acid imine and chromopyrrolic acid as biosynthetic intermediates. A tetrameric hemoprotein synthesizes chromopyrrolic acid, and cytochrome P450 peroxidase catalyzes the intramolecular C–C coupling and decarboxylation of chromopyrrolic acid to form the indolocarbazole core. Goadsporin is a thiopeptide containing thiazole and oxazole heterocyclic rings. The structural gene godA is ribosomally translated to a goadsporin precursor peptide, and oxazole, methyloxazole, and thiazole rings are derived from serine, threonine, and cystein through post-translational modifications. On the basis of these knowledges, a wide variety of indolocarbazole and goadsporin analogs through the rational gene recombination and disruption of these biosynthetic genes were successfully produced.     

Structurally Diverse Metabolites from the Marine-Derived Streptomyces sp. DS-27 Based on Two Different Culture Conditions

Nine new compounds, including streptothiomycin A−E ( 1 – 5 ), two cyclopentenones ( 6 , 7 ), one α-pyrone ( 8 ), wailupemycin Q ( 20 ), along with sixteen known compounds were identified from a rhizosphere strain Streptomyces sp. DS-27 derived from the marine cordgrass Spartina alterniflora under two different culture conditions. All of the structures were elucidated by extensive analysis of 1D/2D NMR and HR-ESI-MS data. The absolute configurations were determined by NOESY analysis, ECD, specific rotation and GIAO NMR calculations, and DP4+ probability analysis. Bioactivity investigation showed that compounds 5 and 7 exhibited significant inhibitory effects on LPS-induced NO production in a dose-dependent manner, which indicates their anti-inflammatory potential.     

海洋细菌9912肽抗生素发酵条件优化研究

对海洋细菌 9912肽抗生素发酵培养基及培养条件进行了研究。结果表明 ,采用廉价的玉米粉、豆饼粉和葡萄糖即可得到良好的效果 ,比实验室培养基提高效价 11%。培养条件为 2 8℃ ,种龄 12h ,接种量 5 % ,发酵周期 2 0h。     

Optimization of Culture Conditions for Fermentation of Soymilk Using Lactobacillus casei by Response Surface Methodology

Soymilk was fermented with Lactobacillus casei, and statistical experimental design was used to investigate factors affecting viable cells of L. casei, including temperature, glucose, niacin, riboflavin, pyridoxine, folic acid and pantothenic acid. Initial screening by Plackett-Burman design revealed that among these factors, temperature, glucose and niacin have significant effects on the growth of L. casei. Further optimization with Box-Behnken design and response surface analysis showed that a second-order polynomial model fits the experimental data appropriately. The optimum conditions for temperature, glucose and niacin were found to be 15.77 °C, 5.23 and 0.63 g/L, respectively. The concentration of viable L. casei cells under these conditions was 8.23 log₁₀ (CFU/mL). The perfect agreement between the observed values and the values predicted by the equation confirms the statistical significance of the model and the model’s adequate precision in predicting optimum conditions.     

用喷雾质谱法分析2种红曲霉所产橙色素的组成

分析了红色红曲霉（Monascus ruber）和烟色红曲霉（Monascus fuliginosus）发酵米粉所产橙色素的喷雾质谱图,发现烟色红曲霉所产橙色素与文献报道的相同;而红色红曲霉所产色素与文献报道不同,其主要组分是分子量分别为340．3和312.3的2种物质。     

Production of formate,acetate, and succinate by anaerobic fermentation of Lactobacillus pentosus in the presence of citrate

Summary The formation of acetate, formate and succinate was studied in Lactobacillus pentosus. These compounds were produced in addition to lactic acid when cells were exposed to anaerobic growth conditions with limited carbohydrates and in the presence of citrate. Citrate was metabolised via oxalacetate serving as an H-acceptor in a joint process together with lactate. The metabolism of citrate resulted in stoichiometric amounts of succinate and acetate. Lactate was degraded to formate and acetate in a reaction catalysed by pyruvate formate lyase. These fermentation products can potentially affect the flavour of fermented food but ecological factors in fermenting meat, e.g. the presence of glucose, nitrate or nitrite prevent this reaction. Offprint requests to: G. Wolf     

Using Phenotype MicroArrays to Determine Culture Conditions That Induce or Repress Toxin Production by Clostridium difficile and Other Microorganisms

Toxin production is a central issue in the pathogenesis of Clostridium difficile and many other pathogenic microorganisms. Toxin synthesis is influenced by a variety of known and unknown factors of genetics, physiology, and environment. To facilitate the study of toxin production by C. difficile, we have developed a new, reliable, quantitative, and robust cell-based cytotoxicity assay. Then we combined this new assay with Phenotype MicroArrays (PM) technology which provides high throughput testing of culture conditions. This allowed us to quantitatively measure toxin production by C. difficile type strain ATCC 9689 under 768 culture conditions. The culture conditions include different carbon, nitrogen, phosphorus, and sulfur sources. Among these, 89 conditions produced strong toxin induction and 31 produced strong toxin repression. Strong toxin inducers included adenine, guanosine, arginine dipeptides, γ-D-Glu-Gly, methylamine, and others. Some leucine dipeptides and the triple-leucine tripeptide were among the strongest toxin repressors. While some results are consistent with previous observations, others are new observations that provide insights into toxin regulation and pathogenesis of C. difficile. Additionally, we have demonstrated that this combined assay technology can be applied broadly to a wide range of toxin producing microorganisms. This study is the first demonstration of simultaneous assessment of a large number of culture conditions influencing bacterial toxin production. The new functional cytotoxin quantitation method developed provides a valuable tool for studying toxigenic microorganisms and may also find applications in clinical and epidemiological research.     

Plantaricins S and T, Two New Bacteriocins Produced by Lactobacillus plantarum LPCO10 Isolated from a Green Olive Fermentation

Twenty-six strains of Lactobacillus plantarum isolated from green olive fermentations were tested for cross-antagonistic activities in an agar drop diffusion test. Cell-free supernatants from four of these strains were shown to inhibit the growth of at least one of the L. plantarum indicator strains. L. plantarum LPCO10 provided the broadest spectrum of activity and was selected for further studies. The inhibitory compound from this strain was active against some gram-positive bacteria, including clostridia and propionibacteria as well as natural competitors of L. plantarum in olive fermentation brines. In contrast, no activity against gram-negative bacteria was detected. Inhibition due to the effect of organic acids, hydrogen peroxide, or bacteriophages was excluded. Since the inhibitory activity of the active supernatant was lost after treatment with various proteolytic enzymes, this substance could be classified as a bacteriocin, designated plantaricin S. Plantaricin S was also sensitive to glycolytic and lipolytic enzymes, suggesting that it was a glycolipoprotein. It exhibited a bactericidal and nonbacteriolytic mode of action against indicator cells. This bacteriocin was heat stable (60 min at 100 degrees C), active in a pH range of 3.0 to 7.0, and also stable in crude culture supernatants during storage. Ultrafiltration studies indicated that plantaricin S occurred as multimolecular aggregates and that the size of the smallest active form is between 3 and 10 kDa. In sodium dodecyl sulfate-polyacrylamide gels, plantaricin S migrated as a peptide of ca. 2.5 kDa. Maximum production of plantaricin S was obtained in a fermentor system in unregulated pH and log-phase cultures of L. plantarum LPCO10 in MRS broth plus 4% NaCl. In these culture conditions, a second bacteriocin (designated plantaricin T) was produced in late-stationary-phase cultures of L. plantarum LPCO10. On the basis of its biological activity, its sensitivity to various enzymes, and its molecular weight (lower than that of plantaricin S) as assessed in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, plantaricin T appeared different from plantaricin S. Curing experiments with L. plantarum LPCO10 resulted in the appearance of variants that no longer produced either of the two bacteriocins but that were still immune to both of them.     

Exopolysaccharides produced by Lactobacillus and Bifidobacterium strains abrogate in vitro the cytotoxic effect of bacterial toxins on eukaryotic cells

Aims: To evaluate the capability of the exopolysaccharides (EPS) produced by lactobacilli and bifidobacteria from human and dairy origin to antagonize the cytotoxic effect of bacterial toxins. Methods and Results: The cytotoxicity of Bacillus cereus extracellular factors on Caco‐2 colonocytes in the presence/absence of the EPS was determined by measuring the integrity of the tissue monolayer and the damage to the cell membrane (extracellular lactate dehydrogenase activity). Additionally, the protective effect of EPS against the haemolytic activity of the streptolysin‐O was evaluated on rabbit erythrocytes. The EPS produced by Bifidobacterium animalis ssp. lactis A1 and IPLA‐R1, Bifidobacterium longum NB667 and Lactobacillus rhamnosus GG were able to counteract the toxic effect of bacterial toxins on the eukaryotic cells at 1 mg ml^?1 EPS concentration. The EPS A1 was the most effective in counteracting the effect of B. cereus toxins on colonocytes, even at lower doses (0·5 mg ml^?1), whereas EPS NB667 elicited the highest haemolysis reduction on erythrocytes. Conclusions: The production of EPS by lactobacilli and bifidobacteria could antagonize the toxicity of bacterial pathogens, this effect being EPS and biological marker dependent. Significance and Impact of the Study: This work allows gaining insight about the mechanisms that probiotics could exert to improve the host health.