Background: Streptococcus mutans and Streptococcus sobrinus are major causative bacterial pathogens of dental caries. Objective: We investigated the applicability of three Lactobacillus strains (L. kefiranofaciens DD2, DD5, and DD6) isolated from kefir and three commercial Lactobacillus strains (L. plantarum ATCC 10012, L. johnsonii JCM 1022, and L. rhamnosus ATCC 7469) as potential oral probiotics with respect to their survivability in an experimental oral environment, antimicrobial activity, and anti-biofilm formation activity against S. mutans and S. sobrinus. Results: Strains DD2, ATCC 10012, ATCC 7469, and JCM 1022 had the best oral survivability, including aerotolerance and enzymatic resistance, and inhibited the growth and biofilm formation of S. mutans and S. sobrinus. In particular, DD2 suppressed all three classes of biofilm formation-associated genes: those associated with carbohydrate metabolism and those encoding regulatory biofilm and adhesion proteins. Conclusions: These results indicate that the novel kefir isolate L. kefiranofaciens DD2 effectively and directly inhibits S. mutans and S. sobrinus.

Lactobacillus kefiranofaciens is the key probiotic bacterium in kefir. In this study, we investigated the effects of oral consumption of L. kefiranofaciens on the fecal quality and intestinal microbiota of mice. Four-week-old Balb/c mice were divided into two groups (n = 8 each) and administered 0.2 mL of saline (control group) or saline containing 2 × 10⁸ cfu L. kefiranofaciens DN1 (LKF_DN1 group) for two weeks. At the end of the experiment, their fecal samples were collected and the fecal quality and microbiota were assessed. The LKF_DN1 group exhibited higher total fecal weight and fecal weight per stool sample than the control group (p < 0.05). Interestingly, the fecal water content was significantly higher in the fecal samples of the LKF_DN1 group than in those of the control group (p < 0.05). The numbers of total bacteria, Firmicutes, Bacteroidetes, Lactobacillus, and Prevotella were significantly higher in the LKF_DN1 group than in the control group (p < 0.05). In contrast, the number of opportunistic pathogens, including Proteobacteria and Enterobacteriaceae, and the percentage of genus Clostridium among the total bacteria were significantly reduced in the LKF_DN1 group (p < 0.05). Our data suggest that regular L. kefiranofaciens DN1 administration could alleviate constipation and improve gut microbiota.

Enterococcus spp. are pathogens that cause environmental mastitis and are difficult to eliminate owing to their resistance to antibiotics. To compare the virulence characteristics of isolates from bovine mastitis milk (BMM) and bovine normal raw milk (NRM), we isolated Enterococcus spp. from 39 dairy farms in South Korea from 2015–2020. A total of 122 Enterococcus spp. were identified, with Enterococcus faecalis (73.8%) accounting for the majority, followed by Enterococcus faecium (26.2%). E. faecalis isolated from BMM harbored gelE, asa1, esp, and cylA genes with a prevalence of 85.7, 71.4, 54.3, and 30.0%, respectively. These genes were significantly more abundant in BMM than in NRM, except for asa1 (p < 0.0001). Interestingly, strong biofilm and gelatinase formation was predominately observed for BMM isolates and this was significantly correlated to the presence of esp and gelE genes (p < 0.05). BMM isolates demonstrated higher resistance to tetracycline (59.3%), followed by chloramphenicol (21.0%), rifampicin (18.5%), doxycycline (4.9%), ciprofloxacin (1.2%), and nitrofurantoin (1.2%), than those from NRM. E. faecalis harboring esp, gelE, and cylA may be causative agents for bovine mastitis and act as a reservoir for the transmission of virulence factors to humans.

Journal of Dairy Science and Biotechnology (J. Dairy Sci. Biotechnol., ISSN 2384-0269; eISSN 2508-3635) publishes original papers or review articles covering topics of chemistry, biotechnology, processing and microbiology of milk and milk products since 1981

Yim JH, et al. J Vet Sci. 2021 Jan;22(1):e11. https://doi.org/10.4142/jvs.2021.22.e11