Characterisation of Enterocins Produced by Antilisterial Enterococcus faecium BH04, BH12, BH84, and BH99 and In Vitro/In Situ Inhibition of Listeria monocytogenes

Abstract

Listeria monocytogenes is a food pathogen that can cause fatal infections, especially in newborns, elderly individuals, and immunocompromised individuals. In recent years, research on novel antibiotics and natural antimicrobial agents of plant or microbial origin has become increasingly important in the face of multiple antibiotic resistance. In this study, enterocins produced by Enterococcus faecium BH04, BH12, BH84, and BH99 were investigated in vitro and in situ as antilisterial agents. The results showed that all strains had bacteriocin activity of 0.4 kAU/mL (400 AU/mL) after 3 h and 25.6 kAU/mL (25600 AU/mL) after 6 h in M17 broth. The strains inhibited the growth of Listeria monocytogenes ATCC 7644 in BHI. Furthermore, E. faecium BH04, BH12, BH84, and BH99 had bacteriostatic potential, whereas enterocins BH04, BH12, BH84, and BH99 had bactericidal potential in a milk model (in situ). The polymerase chain reaction results revealed that all strains had entA, entB, and entP genes encoding enterocin but not the entL50 gene. The enterocins BH04, BH12, BH84, and BH99 retained their antilisterial activity up to 100°C (10 min), up to pH 10, and against catalase, lysozyme, and all chemicals used in this study. On the other hand, ultraviolet light reduced the antilisterial activity of enterocin BH12 by 75% and that of enterocin BH04, BH84, and BH99 by 50%. It was concluded that E. faecium BH04, BH12, BH84, and BH99 could be used as a co-culture in fermented products and that enterocins produced by the strains could be used as antilisterial agents.