Clostridioides difficile is a spore‐forming, Gram‐positive, anaerobic pathogen that caused gastrointestinal illness. During dysbiosis, overgrowth of C. difficile resulting in higher levels of toxin production. Since Lactobacillus has been commonly used to alleviate gastrointestinal discomfort, this study aimed to investigate the effects of Lactobacillus isolated from kimchi on the quorum‐sensing and virulence factors of C. difficile 027. Among the isolated Lactobacillus strains, the acid and bile tolerant L. fermentum Lim2 was only able to reduce C. difficile 027 growth by one log10 CFU per ml. In keeping with this finding, C. difficile 027 growth was unaffected by either untreated or heat‐inactivated cell extracts from L. fermentum Lim2. Both untreated and heat‐inactivated cell extracts did, however, significantly reduce the autoinducer‐2 (AI‐2) activity of C. difficile 027, with the most prominent suppression effect (654‐fold) being found from 100 mg ml−1 of heat‐inactivated cell extract. A gene expression analysis indicated that in the presence of 100 mg ml−1 heat‐inactivated cell extract, the quorum‐sensing (luxS) and the virulence factors (tcdA, tcdB and tcdE) were significantly suppressed, whereas the negative regulator gene (tcdC) was significantly up‐regulated. Taken together, the significant anti‐pathogenic effect from L. fermentum Lim2 could potentially be used to treat C. difficile‐infections. Significance and Impact of the Study Clostridioides difficile is a Gram‐positive pathogenic bacteria that caused gastrointestinal illness via toxic production. The emergence of highly virulence and foodborne C. difficile strains has further increased the incident and severity of C. difficile‐infections (CDIs). Numerous studies have reported the immunomodulatory activity of Lactobacillus, a member of healthy gut microbiota, to maintain gastrointestinal health. Here, we successfully isolated L. fermentum Lim2 from kimchi, and identified a promising anti‐pathogenic effect against C. difficile 027, from the heat‐inactivated L. fermentum cell extract via suppression on the C. difficile 027 quorum‐sensing system and toxin production, which could potentially be used to treat and prevent CDIs.

The integrity of gut barrier functions is closely associated with the pathogenesis of colitis. It is speculated that Lactobacillus brevis Bmb6 alleviates colitis by improving the tight junction (TJ) of the inflamed intestinal epithelial layer. In the present study, the regulatory effects of L. brevis Bmb6 on the TJ barrier to ameliorate colitis-symptoms were investigated. Preliminary screening showed that L. brevis Bmb6 exhibited strong acid and bile acid tolerance, along with antioxidants and β-galactosidase activities. In a 14-day dextran sulfate sodium (DSS)-induced colitis mouse model, treatment with L. brevis Bmb6 significantly decreased in the disease activity index score. In addition, histological analyses showed that treatment with L. brevis Bmb6 protected the structural integrity of the intestinal epithelial layer and mucin-secreting goblet cells from DSS-induced damage, with only slight infiltration of immune cells. Interestingly, western blotting analyses showed that the expression of the TJ protein, zona occluden-1, was restored in Bmb6-treated mice, but not in DSS-induced mice. Consistently, the gene expression of inflammatory cytokines (tumor necrosis factor-α and interferon-γ) was also suppressed in the Bmb6-treated mice. Hence, our findings suggest that suppression of inflammatory conditions enhanced expression of TJ protein, ZO-1, or vice versa, contributing to a colitis-ameliorating effect in L. brevis Bmb6.

The adhesion of intestinal bacteria to the mucus layer is an important colonization strategy in the gut environment. Generally, the bacterial adhesion process is a characteristic feature of the individual cell surface-associated adhesion factors secreted by a particular bacterium.