Ribotype diversity of Listeria monocytogenes strains associated with outbreaks of listeriosis in ruminants.

Ribotyping is a molecular method for the characterization, identification, and typing of bacterial isolates that has value in epidemiological studies. To demonstrate the utility of this technique for typing of Listeria monocytogenes, four outbreaks of epizootic listeriosis in ruminants were investigated through coordinated detection and characterization methods utilizing classical microbiology and nucleic acid-based techniques. L. monocytogenes strains isolated from clinical samples and the silage consumed by the affected animals were ribotyped to establish the causal relationship between feed and the disease outbreak. For all but one outbreak, we were able to isolate L. monocytogenes strains represented by the same ribotype from both clinical and silage samples. Additional L. monocytogenes strains with ribotypes different from those of the respective clinical samples were isolated from all silage samples. This indicates that a diverse population of L. monocytogenes strains exists in farm environments, of which some may be more likely than others to cause disease.