Pathogenicity of Foodborne, Environmental and Clinical Isolates of Listeria Monocytogenes in Mice

Abstract

ABSTRACTFoodborne, environmental and clinical isolates of Listeria monocytogenes and other Listeria species were screened for pathogenicity in immunocompromised mice. Of 218 isolates of L. monocytogenes, 203 were pathogenic and 15 were nonpathogenic. All non‐monocytogenes species were nonpathogenic. Pathogenic isolates were hemolytic for sheep blood. In contrast, many nonpathogenic isolates were weakly hemolytic, but were CAMP positive. Lethal doses (LD50) of pathogenic isolates were 5‐480 cells for immunocompromised mice and 7.2 × 105 to 8.4 × 107 for nonimmunocompromised mice; whereas LD50s for nonpathogenic isolates were > 108 cells in both immunocompromised and nonimmunocompromised mice. Selected test isolates of L. monocytogenes were serotyped; the most common serotypes were 1/2b, 1/2a, 3a and 4b. The initial source and serotype of the isolate appeared not to be related to pathogenicity in immunocompromised mice. However, hemolytic activity was related to pathogenicity.