Sensitivity and Resistance of Listeria monocytogenes ATCC 19115, Scott A, and UAL500 to Nisin.

Listeria monocytogenes ATCC 19115, Scott A, and UAL500 were evaluated for sensitivity to nisin (0 to 50 μg/ml) using a direct plating method. Nisin (10 μg/ml) decreased an initial population of L. monocytogenes (109 CFU per ml) by 6- to 7-log cycles. Sensitivity to nisin was enhanced by addition of 2% NaCl or by reduction of the medium pH from 6.5 to 5.5 with either hydrochloric or lactic acid. Mutants resistant to 50 μg/ml nisin were detected at frequencies of 10-6 to 10-8. Nisin-resistant L. monocytogenes mutants should be expected to arise when nisin is used as an antimicrobial in food systems.