Effect of Temperature, Relative Humidity, and Suspending Menstrua on the Resistance of Listeria monocytogenes to Drying.

The ability of Listeria monocytogenes to survive dehydrated storage at different temperatures (5 vs. 25°C) and relative humidities (75, 59, 35, 14, and 1%) when suspended in different menstrua was studied. L. monocytogenes survived longer when held at 5°C compared to 25°C, and when suspended in beef extract, glycerol, Karo syrup, skim milk, and canned milk compared to distilled water. The contribution of relative humidity to survival was less clear, though survival tended to be longer at the lower relative humidities. At 5°C when suspended in beef extract and held at relative humidities of 59% and below, there was less than a 2 log decline in the viable population (starting count ca. 10/coverslip). L. monocytogenes was not injured during drying or storage at the various relative humidities. In addition, based on the Listeria selective media evaluated, these Listeria media permitted quantitative recovery of the organism dried on surfaces. These results suggested that once L. monocytogenes has contaminated a food processing plant, it can persist for long periods in the plant environment if the temperature is low and the organism is protected by various food components.