Bacteriocinogenic properties and safety evaluation of Enterococcus faecium YT52 isolated from boza, a traditional cereal based fermented beverage

Abstract

The objectives of this study were to characterize the antibacterial substances produced by Enterococcus faecium YT52 isolated from boza, and to evaluate the safety of this strain. E. faecium YT52 inhibits various Gram-positive bacteria, including foodborne pathogens such as Listeria monocytogenes and Bacillus cereus. The manner of action of its antibacterial activity, using proteolytic enzymes, indicate that it produces a bacteriocin. The bacteriocin producing isolate E. faecium YT52 was identified using 16S rRNA gene homology and species-specific polymerase chain reaction (PCR) analysis. The bacteriocin was found to be heat stable and active under both acid and alkaline conditions. The bacteriocin showed primary metabolite kinetics and a bactericidal mode of action against L. monocytogenes. Although enterocin A, B and X genes were detected in E. faecium YT52 by PCR, only one active peptide band (~ 5.5 kDa) with a molecular weight similar to enterocin B was identified by tricine–SDS-PAGE analysis. A safety evaluation of E. faecium YT52 indicated that it is nonhemolytic, gelatinase-negative, and susceptible to clinically relevant antibiotics such as ampicillin, tetracycline and vancomycin. It contains a small number of virulence factors (efaAfm, silent gelE) and antibiotic resistance genes (ermB, tetM, tetL). In conclusion, bacteriocinogenic E. faecium YT52 was found to have a low risk profile, and it may be potentially valuable as a protective culture in the food industry.