Several people from a picnic came down with a gastrointestinal disturbance, and public health officials suspected a case of food poisoning.The food, especially hot dogs, were cultured and after 24 hours of growth on sheep blood agar (SBA), there was a small, round, smooth, translucent colony surrounded by a narrow zone of b-hemolysis.A Gram stain showed gram-positive coccobacilli.Motility medium was inoculated and an umbrella pattern of motility was observed at room temperature.What organism was isolated as the cause of the illness?

Question

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L.monocytogenes is catalase positive and motile at room temperature, which along with b-hemolysis excludes corynebacteria.In wet mount preparations, L.monocytogenes exhibits "tumbling motility" when viewed microscopically.In motility medium, the characteristic "umbrella" pattern is seen when the organism is incubated at room temperature.

Several People from a Picnic Came Down with a Gastrointestinal