Inactivation and Injury of Listeria monocytogenes in a Minimal Medium as Affected by Benzoic Acid and Incubation Temperature

The population of Listeria monocytogenes in a minimal medium (lacking a nitrogen source) at pH 5.5 decreased logarithmically during incubation. Rate of death of the pathogen, indicated by D-values, was greatly affected by changes in the temperature of incubation (4–35°C), but to a much lesser extent by the presence of benzoic acid (3000 ppm). Injury of L. monocytogenes during incubation was equally detectable on tryptose agar containing 6% salt and McBride Listeria Agar containing 0.5% lithium chloride. A greater degree of injury was detected at the lower than the higher temperatures of incubation, but presence of benzoic acid (3000 ppm) did not seem to affect the extent of injury.