Isolation and characterization of a new bacteriocin from Lactobacillus gasseri KT7

A bacteriocin-producing Lactobacillus gasseri strain, KT7, was isolated fro m infant faeces. The supernatant fluid showed inhibitory activity not only against some lactic acid bacteria but also, against some pathogenic and foo d-spoilage species, including Clostridium, Listeria and Enterococcus. An an timicrobial peptide designated gassericin KT7 was isolated from Lactobacill us gasseri KT7. It was purified to homogeneity by a single four-step proced ure: a crude supernatant fluid obtained from early stationary-phase culture in MRS medium was subjected to ammonium sulphate fractionation, CM-Sephade x cation-exchange chromatography, Phenyl-Sepharose hydrophobic chromatograp hy and reverse-phase HPLC chromatography. Gassericin KT7 was sensitive to p roteolytic enzymes, resistant to heat, active over a wide range of pH, and migrated as a 4.5-5.0 kDa peptide on SDS-PAGE. The bacteriocin was produced constitutively during exponential growth. It was bactericidal to sensitive cells and the bactericidal effect was not produced by cell lysis. The amin o acid composition of the bacteriocin was determined and no modified amino acid was found among the residues identified.