Isolation of Listeria spp. from Feces of Feedlot Cattle

Healthy feedlot beef cattle were surveyed for the presence of Listeria spp. in fecal grab samples taken over 3 months. Composite samples were made from 224 individual animals each month. Listeria monocytogenes was isolated from one composite sample (4%) from the first sampling and not from the subsequent two. Listeria innocua was found in composite samples from all three samplings at levels of 17, 9, and 35%, respectively. From the individual samples comprising the Listeria spp.--positive composites, L. monoytogenes was isolated from one sample (3%) in the second sampling but not in the first or third samplings. L. innocua was found in 9, 8, and 10% of the individual samples comprising Listeria --positive composites in the first, second, and third samplings, respectively. The two L. monocytogenes isolates were pathogenic to mice. Further characterization of these isolates revealed atypical rhamnose fermentation patterns. These results indicate that the frequency of isolation of L. monocytogenes from feedlot beef cattle is low.