Intragastric inoculation with a cocktail of Listeria monocytogenes strains does not potentiate the severity of infection in A/J mice compared to inoculation with the individual strains comprising the cocktail.

Although multistrain cocktails of Listeria monocytogenes are used in food inoculation experiments, no studies, to our knowledge, have been reported that use these cocktails in an intragastric mouse model. In this study, we used a five-strain L. monocytogenes cocktail consisting of strains Scott A, MFS108, 101M, V7, and 310 and a four-strain L. monocytogenes cocktail containing strains Scott A, EGD, H7738, and F2365. Here, we report that intragastric inoculation of anesthetized mice with approximately 106 CFU of a cocktail of L. monocytogenes strains does not result (P > 0.05) in a more severe infection (on the basis of the CFU of Listeria spp. recovered from the spleen, liver, and blood) than inoculation of mice with similar numbers of the individual strains comprising the cocktail. Nor did we observe any consistent relationship between susceptibility of L. monocytogenes strains to inactivation in synthetic gastric fluid in vitro and virulence in mice.