Acid-adapted Listeria monocytogenes displays enhanced tolerance against the lantibiotics nisin and lacticin 3147

Log-phase Listeria monocytogenes cells become tolerant to a variety of envi ronmental stresses following acid adaptation at pH 5.5. We demonstrated tha t adapted cells also exhibit increased tolerance to nisin and, to a lesser extent, lacticin 3147. At nisin concentrations of 100 and 200 IU/ml the sur vival of acid-adapted cells was approximately 10-fold greater than nonadapt ed cells. However, acid adaptation had only a moderate effect on the tolera nce of L. monocytogenes to lacticin 3147, a phenomenon that possibly reflec ts the distinct mode of action of this bacteriocin. Analysis of the fatty a cid composition of the bacterial membrane indicated that straight-chain fat ty acids C14:0 and C16:0 were significantly increased in acid-adapted cells while levels of C18:0 decreased. The results indicate that stress mechanis ms that are induced in mildly acidic conditions provide protection against the antimicrobial action of bacteriocins. This increased resistance of acid -adapted L. monocytogenes could cause increased survival of this pathogen i n food products in which nisin or other bacteriocins are used as preservati ves.