Studies on the growth of Listeria monocytogenes and Lactobacillus casei in mixed cultures

The effect of lactic acid production of Lactobacillus casei on the growth characteristics of Listeria monocytogenes was examined in milk. The effect of temperature (7, 13, 20 °C) and the co-ratios with Lb. casei at different cell count ratios (10:1, 100:1, 10 000:1) on the growth of L. monocytogenes were studied. At a 10 000:1 ratio induction of an early stationary phase of L. monocytogenes occurred. An exponentially decreasing correlation was observed between the logarithmic maximum population of L. monocytogenes and the initial log counts of lactobacilli. The Baranyi model was fitted to the obtained growth curves. The Baranyi equation provided good fit for the lag and exponential phase of L. monocytogenes. According to our observations, pH decrease does not seem to be the main factor of early stationary phase induction of L. monocytogenes in milk