Serological groups among untypable bovine isolates of Pasteurella haemolytica

Ten Pasteurella haemolytica isolates from the nasal passages of cattle, untypable by the indirect hemagglutination procedure, were grouped into three serotypes by the rapid plate agglutination procedure. Serological specificity and serum absorption results showed that the 10 indirect hemagglutination-negative isolates belonged to three distinct serotypes and were not members of established serotypes that lack the specific soluble antigen that forms the basis of serotyping by indirect hemagglutination. All isolates were biotype A.