An allelopathy based model for the Listeria overgrowth phenomenon.

In a standard procedure of food safety testing, the presence of the pathogenic bacterium Listeria monocytogenes can be masked by non-pathogenic Listeria. This phenomenon of Listeria overgrowth is not well understood. We present a mathematical model for the growth of a mixed population of L. innocua and L. monocytogenes that includes competition for a common resource and allelopathic control of L. monocytogenes by L. innocua when this resource becomes limited, which has been suggested as one potential explanation for the overgrowth phenomenon. The model is tested quantitatively and qualitatively against experimental data in batch experiments. Our results indicate that the phenomenon of masked pathogens can depend on initial numbers of each population present, and on the intensity of the allelopathic effect. Prompted by the results for the batch setup, we also analyze the model in a hypothetical chemostat setup. Our results suggest that it might be possible to operate a continuous growth environment such that the pathogens outcompete the non-pathogenic species, even in cases where they would be overgrown in a batch environment.