Characterisation of Pasteurella multocida associated with bovine respiratory disease in Hungary

Pasteurella multocida is a Gram-negative bacterium with a broad host range. This opportunistic pathogen is a common inhabitant of the upper respiratory tract of various mammal and avian species. In the presence of predisposing factors, it causes several diseases, which lead to major welfare problems and remarkable economic losses. The association of P. multocida and bovine respiratory disease complex (BRDC) has been well known since the early 1950s. Despite the using of efficient vaccines against other respiratory pathogens, the increased number of cases suggests that P. multocida have a definite role in the etiology of BRDC. The aim of our study was to characterize 39 P. multocida strains of bovine origin isolated from different herds in Hungary. The studied strains represented only three serotypes: A:3, A:3,4, and A:4. The most frequent biovars, determined by their sugar fermentation abilities and enzyme activities, were biovar 2 (33%) and 3 (44%). Their subspecies were defined with biochemical tests and molecular methods (M13 PCR, 16S rDNA PCR-RFLP). These methods delineated two dominant groups (I and II). Group I consisted of strains belonging to biovar 2, they showed α-glucosidase activity and presented type „B” M13 profile. Whereas group II contained strains with biovar 3, and type „A” M13 profile without α-glucosidase activity. The existence and separation of these groups were confirmed by ERIC-PCR. Looking at the diagnostic background, all strains in group I were associated with pneumonia while the strains in group II originated from various clinical cases. The filamentous hemagglutinin (pfhA) that plays an important role in the early colonization of the respiratory tract could only be detected in group I. It may explain why these strains were isolated from cases of bovine pneumonia.