Ursoricin, a bacteriocin of , has potent activity against methicillin-resistant and vancomycin-resistant enterococci.

Unlabelled: The emergence of drug-resistant bacteria, particularly methicillin-resistant (MRSA) and vancomycin-resistant enterococci (VRE), has increased the need to discover novel antimicrobial agents that are effective against these species. Here, we describe the identification and purification of the mutacin BHT-B-like gene locus and bacteriocin peptide from , which is closely related to ; hence, we named this bacteriocin ursoricin. Ursoricin is a cationic, chromosome-encoded peptide that has potent antimicrobial effects against Gram-positive pathogens, including MRSA and VRE, with minimum inhibitory concentrations in the micromolar range. Ursoricin also inhibits the biofilm formation of high biofilm-forming . Antibacterial activity was retained after treatment at 100°C for 60 min at a pH range of 3-9 and was partially reduced by treatment with proteinase K for 2 h (63% residual activity). The potent anti-MRSA, anti-VRE, and antibiofilm effects of ursoricin suggest that it is a possible candidate for the treatment of MRSA, VRE, and biofilm-associated infections.

Importance: The emergence of multidrug-resistant bacteria worldwide has posed a significant public health threat and economic burdens that make the identification and development of novel antimicrobial agents urgent. Bacteriocins are promising new agents that exhibit antibacterial activity against a wide range of human pathogens. In this study, we report that the bacteriocin produced by showed good antibacterial activity against a wide range of and enterococcus strains, particularly methicillin-resistant , vancomycin-resistant enterococci, and high biofilm-forming . Interestingly, this bacteriocin had a stronger effect on than on , which is a major commensal bacterium in human skin; this result is important when considering the disturbance of bacterial flora, especially on the skin, mediated by the application of antibacterial agents.