COMPARATIVE-STUDIES OF CLASS IIA BACTERIOCINS OF LACTIC-ACID BACTERIA

Four class IIa bacteriocins (pediocin PA-1, enterocin A, sakacin P, an d curvacin A) were purified to homogeneity and tested for activity tow ard a variety of indicator strains. Pediocin PA-1 and enterocin A inhi bited more strains and had generally lower MICs than sakacin P and cur vacin A. The antagonistic activity of pediocin-PA1 and enterocin ii wa s much more sensitive to reduction of disulfide bonds than the antagon istic activity of sakacin P and curvacin A, suggesting that an extra d isulfide bond that is present in the former two may contribute to thei r high levels of activity. The food pathogen Listeria monocytogenes wa s among the most sensitive indicator strains for all four bacteriocins . Enterocin A was most effective in inhibiting Listeria, having MICs i n the range of 0.1 to 1 ng/ml. Sakacin P had the interesting property of being very active toward Listeria but not having concomitant high l evels of activity toward lactic acid bacteria. Strains producing class IIa bacteriocins displayed various degrees of resistance toward nonco gnate class IIa bacteriocins; for the sakacin P producer, it was shown that this resistance is correlated with the expression of immunity ge nes. It is hypothesized that variation in the presence and/or expressi on of such immunity genes accounts in part for the remarkably large va riation in bacteriocin sensitivity displayed by lactic acid bacteria.