Abstract

Fermented pork rolls and stinky tofu are healthy fermented foods produced in Vietnam for a long time. These foods have proven to be a rich source for probiotic isolation studies. In this study, four Enterococcus strains were isolated from fermented pork roll (F20BA, F26B) and stinky tofu (F53BA, F54BA) using specific selection media. Phylogenetic and ribosomal multilocus sequence typing analysis confirmed that these strains are Enterococcus lactis. Besides, the safety and probiotic properties of these strains were evaluated. Antimicrobial susceptibility testing and polymerase chain reaction (PCR) analysis confirmed all four strains were vancomycin-susceptible and lacked resistance genes (vanA and vanB). Hemolytic activity was assessed using blood agar plates, verifying the isolates were non-hemolytic. PCR amplification and genome sequencing further indicated that these strains do not contain common virulence-encoding genes. In addition, the isolates exhibit important probiotic properties. They can survive and grow in an de Man, Rogosa and Sharpe medium with low pH (2.5) and in the presence of 1% bile salts. Disk diffusion tests confirmed their ability to inhibit enteropathogenic bacteria, including Escherichia coli, Salmonella, Shigella, Staphylococcus aureus, and Listeria. Additionally, all strains demonstrated cholesterol assimilation ability in in-vitro conditions. These bacterial strains are undergoing further research for potential development into probiotic products.

Key words: Keywords: Enterococcus, Enterococcus lactis, Enterococcus faecium, probiotic, fermented pork roll, stinky tofu.