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Enterococcus hirae HM02-04 isolated from breast milk exerted growth inhibition against especially vancomycin resistance enterococci (VRE). The aims of this study were to purify and characterize the antimicrobial substance produced by the strain HM02-04. One active peptide was successfully purified by 3 steps of Amberlite XAD-16 adsorption-desorption, cation exchange chromatography, and reverse-phase HPLC. It had 2605.298 Da peptide by MALDI-TOF MS analysis. The peptide sequence determined by LC-MS/MS contained only 23 amino acid residues providing the molecular mass of 2312.67 Da by in silico analysis. However, its amino acid sequence obtained showed no homology to other bacteriocins including enterocins previously reported and proposed as a novel one named Hiracin HM02-04. This is the first report to discover E. hirae isolated from breast milk that was able to produce a bacteriocin against VRE. Hiracin HM02-04 was stable at a high temperature of 121°C for 15 min and at a wide pH range of 3–9. It was sensitive to actinase E, pepsin, proteinase K and trypsin. The Hiracin HM02-04 has the narrow inhibition spectrum and no inhibition against Listeria. This bacteriocin was also found to have a bactericidal mode of action with concomitant cell lysis against the strain VRE 426. The present research addresses Hiracin HM02-04 as a promising alternative to conventional antibiotics in the treatment of enterococcal infections.
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