ABSTRACT

Listeria monocytogenes is a member of the family Corynebacteriaceae, order Eubacteriales. It is a small, slightly curved gram-positive and catalase-positive bacillus with rounded ends. The organism can exist in both a rough form and the predominantly pathogenic smooth form that is characterized by a peritrichous arrangement of flagella. These flagella are responsible for the tumbling motility seen when the organism is grown in cultures at room temperature. Old cultures, particularly if incubated at 37C, show imperceptible movement. The organism ferments several carbohydrate substances; however, the fermentative reactions are neither sufficiently characteristic nor consistent enough to be of much diagnostic significance. L. monocytogenes produces soluble hemolysins that may cause a very narrow band of beta-hemolysis on blood agar plates.