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Listeria monocytogenes is a bacterium that infects livestock and humans. We report the first outbreak of invasive listeriosis caused by L. monocytogenes in a guinea pig breeding colony. Eighty to 100% mortality rate was recorded in the colony of 80 guinea pigs within four weeks outbreak. On epidemiologic investigation, Listeria monocytogenes cultures were made by direct plating of affected organs on Oxford- Listeria selective agar. Culture of suspected cabbage in University of Vermont Listeria-selective broth and Oxford- Listeria selective agar yielded Listeria monocytogenes. Characterization of Listeria species from the clinical and environmental samples cabbage revealed Listeria monocytogenes serotypes 4b.The histological preparations of the liver and lung tissues specimens revealed severe congestion of vessels, multifocal pale areas made up of aggregates of vacuolated hepatocellular necrosis and hemorrhagic interlobular septa with severe fibroplasia around the bronchial walls. Gram-positive thick short-rods were observed. Based on the clustering of cases within the space of time and serotype data from the clinical tissues and cabbage, it was concluded that the cabbage is the possible source of acquisition of infection in the guinea pig breeding colony. Thus, the consumption of fresh or undercooked green foods (cabbage, lettuce and others) that have been grown using animal manure contaminated with Listeria monocytogenes may increase the risk of listeriosis in susceptible animals and humans.
Keywords: Guinea pigs, cabbage, Listeria monocytogenes, listeriosis, septicemia, abortion
> Animal Production Research Advances Vol. 2 (4) 2006: pp. 248-252