Antagonistic activity of Lactobacillus acidophilus ATCC 4356 S-layer protein on Salmonella enterica subsp. enterica serovar Typhimurium in Caco-2 cells

Lactic Acid Bacteria Surface Proteins in the Mechanisms of Cell Adhesion and Immunoregulation

This study delves into the role of lactic acid bacteria (LAB) surface proteins in cell adhesion and immunoregulation. Using fluorescence microscopy, we observed distinct adhesion patterns on various cell types. LAB surface proteins demonstrated concentration-dependent inhibition of Salmonella adhesion, with LAB69 exhibiting potent antagonistic effects. Genetic expression analysis revealed nuanced responses in key genes (MD2, TLR4, IL-10, MUC3, MIF) across different cell types, highlighting the diverse immunomodulatory effects of LAB surface proteins. Modulation of pro-inflammatory (TNF-α) and anti-inflammatory (IL-10) cytokines further emphasized the complex interplay. In conclusion, this study underscores the pivotal role of LAB surface proteins in mediating cell adhesion and immunoregulation, providing a foundation for isolating specific immunomodulatory molecules within LAB surface proteins for potential applications in microbial ecological agents.

Host-microbe interaction and pathogen exclusion mediated by an aggregation-prone surface layer protein of Lactobacillus helveticus

Probiotic surface layer proteins (Slps) have multiple functions and bacterial adhesion to host cells is one of them. The precise role of Slps in cellular adhesion is not well understood due to its low native protein yield and self-aggregative nature. Here, we report the recombinant expression and purification of biologically active Slp of Lactobacillus helveticus NCDC 288 (SlpH) in high yield. SlpH is a highly basic protein (pI = 9.4), having a molecular weight of 45 kDa. Circular Dichroism showed a prevalence of beta-strands in SlpH structure and resistance to low pH. SlpH showed binding to human intestinal tissue, enteric Caco-2 cell line, and porcine gastric mucin, but not with fibronectin, collagen type IV and laminin. SlpH inhibited the binding of the enterotoxigenic E. coli by 70 % and 76 % and that of Salmonella Typhimurium SL1344 by 71 % and 75 % to enteric Caco-2 cell line in the exclusion and competition assays, respectively. The pathogen exclusion and competition activity and tolerance to harsh gastrointestinal conditions show the potential for developing SlpH as a prophylactic or therapeutic agent against enteric pathogens.

A Quadruple Coating of Probiotics for Enhancing Intestinal Adhesion and Competitive Exclusion of Salmonella Typhimurium

Previously, our group showed that a quadruple coating of probiotics resulted in higher survivability of probiotics under high acid, bile salt, and thermal stresses. In this study, we evaluated the effect of the quadruple coating of probiotics on adhesive properties as well as on competitive exclusion of Salmonella Typhimurium in Caco-2 cells. We found that the quadruple coating of probiotics exhibited an overall increased adhesion property (up to 10.8-fold) and increased competitive exclusion of Salmonella Typhimurium (up to 4.3-fold). Thus, this study has significant implications and can lead to the development of methods that can improve the adhesive ability of probiotics as well as the adhesive inhibition of pathogens.

Protective function of surface layer protein from Lactobacillus casei fb05 against intestinal pathogens in vitro

Escherichia coli and Salmonella are common pathogenic bacteria in human intestine, which can infect epithelial cells and cause diseases. Adhesion to intestinal tissue is the first step of pathogen infection. This work was to investigate the protective function of surface layer protein (SLP) from Lactobacillus casei fb05 against the harmful effects of E. coli and Salmonella on intestinal tissue (collagen and HT-29 cells). The SLP of L. casei fb05 was identified by transmission electron microscopy and SDS-PAGE. The purified SLP could reduce the adhesion of E. coli and Salmonella to collagen and HT-29 cells as observed by light microscope. The flow cytometry results showed that the L. casei fb05 SLP decreased the two pathogens-induced apoptosis of HT-29 cells by about 45%-49%. In addition, the activation of caspase-9 and caspase-3 caused by the two pathogens was significantly declined by the interference of the L. casei fb05 SLP. All the findings demonstrated that the L. casei fb05 SLP could decrease the deleterious effects of E. coli and Salmonella on intestinal tract in two ways: reducing pathogen adhesion and inhibiting pathogen-induced apoptosis. The potential of L. casei fb05 SLP in the treatment of intestinal diseases might be explored in this work.

Functional Properties of Food Origin Lactobacillus in the Gastrointestinal Ecosystem-In Vitro Study

In the current study, the probiotic activity of ten Lactobacillus (Lb.) strains, previously isolated from the traditional Polish fermented vegetable, was characterized. Strains were assessed for adhesion to human intestinal epithelial Caco-2 cells and regulation of selected cytokine production (IL-1β, IL-6, IL-10, IL-23, and TNF-α) by THP-1 macrophages. The effect of tested strains on Caco-2 cell apoptosis was also investigated using a caspase-3 assay. Adhesion capacity was strain-dependent (1.29-8.24% of initial population). Highest adhesion was observed for Lb. brevis O24. All Lactobacillus strains investigated in this study stimulated two- to threefold increase in TNF-α, IL-1β, and IL-6 production, compared to the control. Additionally, selected strains of Lactobacillus caused a significant decrease of pro-inflammatory cytokine production by lipopolysaccharide (LPS)-stimulated THP-1 cells. Almost all Lactobacillus investigated in this study are potent stimulators of IL-10 production. All tested Lactobacillus cells slightly increased the caspase-3 activity in Caco-2 cells. Lb. casei O18 was the most inducing strain. The tested strains had no effect on staurosporine (STS)-induced caspase-3 activity. According to these results, the most promising strains are Lb. plantarum O20, two strains Lb. brevis O22 and O24, and Lb. rhamnosus K3. These newly identified lactobacilli hold promise for use as probiotics in functional food applications.

Lactobacillus acidophilus S-layer protein-mediated inhibition of PEDV-induced apoptosis of Vero cells

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Lactobacillus S-layer protein plays an inhibitory role during PEDV infection.

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In Vero cells infected with PEDV, apoptosis was mediated by caspase-8/3 activation.

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Lactobacillus S-layer protein inhibited PEDV-induced apoptosis in Vero cells.

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S-layer protein reduced caspase-8/3 activation against PEDV-induced apoptosis.

To gain insight into the mechanism of Lactobacillus acidophilus (L. acidophilus) S-layer protein antiviral activity, we examined how S-layer protein impacts porcine epidemic diarrhea virus (PEDV) infection and PEDV-induced apoptosis of Vero cells. Pretreatment (exclusion assay), coincubation (competition assay), and post-treatment (displacement assay) of PEDV-infected Vero cells with the S-layer protein was examined. Interestingly, significant inhibition of PEDV by S-layer protein was only observed in the exclusion assay. In Vero cells infected with PEDV, we found that apoptosis was mediated by activation of caspase-8 and caspase-3 in the late stage of infection. When PEDV-infected Vero cells were pretreated with S-layer protein, rates of Vero cell apoptosis were markedly decreased and cell damage was significantly reduced, as evaluated by flow cytometry and microscopy. Detailed analyses showed that the S-layer protein inhibited caspase-8 and caspase-3 activity. Taken together, our results suggest that L. acidophilus S-layer protein plays an inhibitory role during PEDV infection of Vero cells, and that the antagonistic activity of the protein is not via competition with PEDV for binding sites. In addition, the findings suggest that L. acidophilus S-layer protein protects against PEDV-induced apoptosis through reduced caspase-8 and caspase-3 activation in the later stages of infection. This mechanism may represent a novel approach for antagonizing PEDV and other viruses.

Anti-adhesion of probiotic Enterococcus faecium WEFA23 against five pathogens and the beneficial effect of its S-layer proteins against Listeria monocytogenes

Enterococcus faecium WEFA23 is a potential probiotic strain isolated from Chinese infant feces. In this study, the antagonistic activity of E. faecium WEFA23 on adhesion to pathogens was investigated. Enterococcus faecium WEFA23 was able to compete, exclude, and displace the adhesion of Escherichia coli O157:H7, Salmonella Typhimurium ATCC 13311, Listeria monocytogenes CMCC54007, Staphylococcus aureus CMCC26003, and Shigella sonnei ATCC 25931 to Caco-2 cells. Among them, L. monocytogenes achieved the strongest inhibition rate in both competition and displacement assays. Those anti-adhesion capacities were related to the bacterial physicochemical properties (hydrophobicity, auto-aggregation, and co-aggregation) of the bacterial surface. For L. monocytogenes, the anti-adhesion capacity was affected by the heat treatment, cell density, and growth phase of E. faecium WEFA23; 10⁸ colony-forming units of viable cells per millilitre at the stationary phase exhibited the strongest anti-adhesion activity. In addition, removal of S-layer proteins of E. faecium WEFA23 by treatment with 5 mol/L LiCl significantly decreased its adhesion capacity, and those S-layer proteins were able to compete, displace, and exclude L. monocytogenes at different levels. Both cells and S-layer proteins of E. faecium WEFA23 significantly reduced the apoptosis of Caco-2 cells induced by L. monocytogenes, which was mediated by caspase-3 activation. This study might be helpful in understanding the anti-adhesion mechanism of probiotics against pathogens.

Inhibition of Shigella sonnei-induced epithelial barrier disruption by surface-layer associated proteins of lactobacilli from Chinese fermented food

Surface-layer associated proteins (SLAP) of Lactobacillus paracasei ssp. paracasei M5-L and Lactobacillus casei Q8-L were examined to identify the functional basis for their protection within intestinal epithelial cells. The results showed that SLAP of M5-L and Q8-L remained active in a trypsin solution and retained a 45-kDa protein band, similar to that observed in controls. In contrast, under conditions of simulated gastric juice, the SLAP were partially degraded. Inhibitory effects of SLAP on adherence of Shigella sonnei to HT-29 cells were assessed with use of exclusion, competition, and replacement assays. In response to M5-L at 50 μg/mL SLAP, an inhibition ratio of 33% was obtained, while for Q8-L at 400 μg/mL SLAP, the inhibition ratio was 48%. Hoechst 33258 test results showed that cells infected with S. sonnei and co-incubated with SLAP of M5-L and Q8-L were only partially apoptotic, with apoptosis rates of 37.67 and 43.67%, respectively. These levels of apoptosis were substantially lower than that observed with cells infected with S. sonnei alone. In addition, the SLAP of Q8-L and M5-L reduced downstream caspase-1 activity and further modified apoptotic cell damage. Finally, SLAP of M5-L and Q8-L were also able to prevent S. sonnei-induced membrane damage by inhibiting delocalization of zonula occludens (ZO)-1 and reducing the amount of occludin produced by S. sonnei.

Antagonistic Activity of Lactobacillus reuteri Strains on the Adhesion Characteristics of Selected Pathogens

Adhesion ability of probiotics is the key factor that decides their colonization in the gastrointestinal tract and potential to inhibit pathogens. Therefore, adhesion ability can be considered as a key determinant for probiotic efficacy. Presents study documents the antagonistic activity of viable/untreated, Lithium chloride (LiCl) treated or heat-killed forms of eight probiotic Lactobacillus reuteri strains on the adhesion characteristics of selected pathogens. All strains investigated were able to adhere to Caco-2 cells. L. reuteri strains tested were able to inhibit and displace (P < 0.05) the adhesion of Escherichia coli ATCC25922, Salmonella typhi NCDC113, Listeria monocytogenes ATCC53135, and Enterococcus faecalis NCDC115. The probiotic strain L. reuteri LR6 showed the strongest adhesion and pathogen inhibition ability among the eight L. reuteri strains tested. In addition, the abilities to inhibit and to displace adhered pathogens depended on both the probiotic and the pathogen strains tested suggesting the involvement of various mechanisms. The adhesion and antagonistic potential of the probiotic strains were significantly decreased upon exposure to 5 M LiCl, showing that surface molecules, proteinaceous in nature, are involved. The heat-killed forms of the probiotic L. reuteri strains also inhibited the attachment of selected pathogens to Caco-2 cells. In conclusion, in vitro assays showed that L. reuteri strains, as viable or heat-killed forms, are adherent to Caco-2 cells and are highly antagonistic to pathogens tested in which surface associated proteins play an important role.

Adhesive ability means inhibition activities for lactobacillus against pathogens and S-layer protein plays an important role in adhesion

Eighty-five strains of lactobacillus were isolated from the pig intestine and identified by sequencing analysis based on 16S rRNA gene, from which five lactobacillus strains with high adhesive ability were selected. The inhibition ability of the five lactobacillus strains with or without S-layer proteins against adherence of Escherichia coli K88 and Salmonella enteritidis 50335 to Caco-2 was evaluated in vitro with Lactobacillus rhamnosus GG strain (LGG) as a positive control. In addition, tolerance of lactobacilli to heat, acid, bile, Zn(2+) and Cu(2+) were assessed. All five selected strains, Lactobacillus salivarius ZJ614 (JN981856), Lactobacillus reuteri ZJ616 (JN981858), L. reuteri ZJ617 (JN981859), L. reuteri ZJ621 (JN981863) and L. reuteri ZJ623 (JN981865), showed inhibition against the two pathogens, E. coli K88 and S. enteritidis 50335. L. reuteri ZJ621 showed higher inhibition ability than the others to S. enteritidis 50335 (P < 0.05). Sodium dodecyl sulfate-Polyacrylamide gel electrophoresis (SDS-PAGE) analysis indicated that all five strains had abundant bands with molecular weight ranging from 34 to 130 KDa as well as had a common band of approximately 42 KDa. After treatment with 5 M LiCl to remove S-layer protein, the inhibition activities of the lactobacilli against pathogens decreased significantly (P < 0.05). The results showed that higher adhesive ability means higher inhibition activity for lactobacillus against pathogen, in which S-layer proteins plays an important role.