Prediction of Listeria monocytogenes growth as a function of environmental factors

Abstract

Listeria monocytogenes is a bacterium widespread in the environment, which has a capacity to survive and grow under various conditions. The bacterial growth results from interactions when subjected to various temperatures, pH levels, and NaCl concentrations were examined by measurements and predictive modelling. Good correlation across the range of growth conditions was shown among observed and predicted growth values, having similar trends and minimal deflections for pH levels 5.0 and 6.0. The growth condition in the 8% NaCl concentration (pH 7.0, temperature 4 °C) resulted with a growth curve of 1 log interval greater than the fitted curve for all the measurements. In all of the cases, there were consistent increases in the rates and decreases in the lag time when the growth temperature increased. Higher incubation temperatures provided higher growth rates as 30 °C and 35 °C yielded double increase of the fitted rate. Fitted and measured growth rates for salinity conditions were significantly different (P<0.05). Comparison of doubling times showed good compatibility, particularly at lower temperatures. Critical use of a model is suggested, although it may enable microbiologists to limit the need of challenge tests and to make rapid and realistic prediction of the growth of L. monocytogenes under conditions relevant to a range of aquatic and other products examined.