Purification and characterization of bacteriocins-like inhibitory substances from food isolated Enterococcus faecalis OS13 with activity against nosocomial enterococci

Nosocomial infections caused by enterococci are an ongoing global threat. Thus, finding therapeutic agents for the treatment of such infections are crucial. Some Enterococcus faecalis strains are able to produce antimicrobial peptides called bacteriocins. We analyzed 65 E. faecalis isolates from 43 food samples and 22 clinical samples in Egypt for 17 common bacteriocin-encoding genes of Enterococcus spp. These genes were absent in 11 isolates that showed antimicrobial activity putatively due to bacteriocins (three from food, including isolate OS13, and eight from clinical isolates). The food-isolated E. faecalis OS13 produced bacteriocin-like inhibitory substances (BLIS) named enterocin OS13, which comprised two peptides (enterocin OS13 alpha OS13 beta) that inhibited the growth of antibiotic-resistant nosocomial E. faecalis and E. faecium isolates. The molecular weights of enterocin OS13 alpha and OS13 beta were determined as 8079 Da and 7859 Da, respectively, and both were heat-labile. Enterocin OS13 alpha was sensitive to proteinase K, while enterocin OS13 beta was resistant. Characterization of E. faecalis OS13 isolate revealed that it belonged to sequence type 116. It was non-hemolytic, bile salt hydrolase-negative, gelatinase-positive, and sensitive to ampicillin, penicillin, vancomycin, erythromycin, kanamycin, and gentamicin. In conclusion, BLIS as enterocin OS13 alpha and OS13 beta represent antimicrobial agents with activities against antibiotic-resistant enterococcal isolates.

Automated summary

Nosocomial infections caused by enterococci are a global threat, and finding therapeutic agents is crucial. Enterococcus faecalis strains can produce bacteriocins, which were absent in some isolates showing antimicrobial activity. Enterocin OS13 alpha and OS13 beta, produced by E. faecalis OS13, inhibited growth of antibiotic-resistant enterococcal isolates.