Serotyping of Mannheimia (Pasteurella) haemolytica isolates from the upperMidwest United States

Mannheimia (Pasteurella) haemolytica biotype A serotype 1 (Al) is the prima ry bacterial agent responsible for the clinical signs and pathophysiologic events in bovine pneumonic pasteurellosis. The goal of this study was to de termine the prevalence of other serotypes of M. haemolytica biotype A organ isms obtained from the upper Midwest diagnostic laboratories. A total of 14 7 M. haemolytica isolates were collected from Minnesota, South Dakota, and Michigan. Isolates were tested against M. haemolytica antisera obtained fro m the National Animal Disease Center, Ames, Iowa. Results indicated that M. haemolytica serotype 1 represented approximately 60%, serotype 6 represent ed 26%, and serotype 2 represented 7% of the total examined isolates. In ad dition, 7% of the isolates were serotype 9, 11, or untypable. This finding suggests that M. haemolytica serotypes other than serotype 1 can be isolate d from the lung lesions of diseased cattle and seem to be capable of causin g the pathologic changes observed in the lung with pneumonic pasteurellosis .