PURIFICATION, PARTIAL CHARACTERIZATION AND MODE OF ACTION OF ENTEROCOCCIN EFS2, AN ANTILISTERIAL BACTERIOCIN PRODUCED BY A STRAIN OF ENTEROCOCCUS-FAECALIS ISOLATED FROM A CHEESE

Enterococcus faecalis strain EFS2, isolated from the surface of a trad itional cheese, produced a bacteriocin active against Gram-positive ba cteria-including Listeria spp and some Staphylococcus aureus strains. The bacteriocin, named enterococcin EFS2, has been purified to homogen eity by ammonium sulphate precipitation and reversed-phase high perfor mance liquid chromatography (RP-HPLC). The molecular weight was determ ined by mass spectrometry to be 7149.6. The amino acid composition of enterococcin EFS2 revealed that it contained 67 amino acid residues an d had a blocked amino-terminal end. Enterococcin EFS2 induced viabilit y loss, efflux of K+ ions and ATP, and cell lysis. Kinetic study of ba ctericidal activity of enterococcin EFS2 on Listeria innocua strain LI N11 indicated slower cell destruction than by nisin. At pH 7.0, the ac tivity of enterococcin EFS2 was the highest at 35 degrees C and was lo st at 15 degrees C. The bacteriocin was more active against L. innocua strain LIN11 in broth adjusted to pH 6.0, 7.0 and 8.0 than to pH 4.5 at 30 degrees C.