Bacteriologic and epidemiologic studies on the occurrence of Listeria monocytogenes in healthy cattles

The incidence of Listeria monocytogenes in 61 fresh stool specimens from normal beef cattle obtained from a slaughterhouse in Rio de Janeiro was studied. The animals were divided in two groups of similar number separated by age; animals of up to five years, and animals of 5 years and more. In the research of this microorganism 9 culture media were used: four enrichment media, one for transport and four selective media. From the results, 11 animals proved to be carriers, of which nine were five years of age or older and two were of the younger group. Two hundred and twenty-one samples of Listeria were obtained from these 11 animals. The combination of Tryptose broth containing 40 mcg/ml nalidixic acid and 10 mcg/ml trypaflavine, incubated for 5 days at ambient temperature (+/- 28 degrees C), with the second modification of Ralovich medium, showed the best results for detection of Listeria both quantitatively and qualitatively. Among the serotypes characterized in this research the types with greater incidence were L 4 a (60.18%), L 4 f (20.36%), and L 4 b (9.05%).