Influence of pH, salt, and temperature on nisin resistance in Listeria monocytogenes

The influence of pH (5.0, 5.5, and 6.0), salt (0.5, 2.0, and 3.5%) and temperature (10, 20, and 30 degrees C) on the frequency of nisin resistance in Listeria monocytogenes Scott A was evaluated. At 20 and 30 degrees C, resistance frequencies of around 1 in 10(5) were obtained regardless of salt concentration or pH. At 10 degrees C the frequency of nisin resistance dropped with decreasing pH and decreasing salt concentration. At pH 5.5 and 0.5% NaCl it became impossible to generate nisin-resistant isolates. Low salt (2 to 3.5%) appeared to play a protective role, allowing L. monocytogenes to better survive nisin at low temperature (10 degrees C).