Suppressive effect of Lactobacillus fermentum Lim2 on Clostridioides difficile 027 toxin production

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.