Distribution of the ompA-types among ruminant and swine pneumonic strains of Pasteurella multocida exhibiting various cap-locus and toxA patterns.

Pasteurella multocida is an important pathogen in food-producing animals and numerous virulence genes have been identified in an attempt to elucidate the pathogenesis of pasteurellosis. Currently, some of these genes including the capsule biosynthesis genes, the toxA and the OMPs-encoding genes have been suggested as epidemiological markers. However, the number of studies concerning ruminant isolates is limited, while, no attempt has ever been made to investigate the existence of ompA sequence diversity among P. multocida isolates. The aim of the present study was the comparative analysis of 144 P. multocida pneumonic isolates obtained from sheep, goats, cattle and pigs by determining the distribution of the ompA-types in conjunction with the cap-locus and toxA patterns. The ompA genotypes of the isolates were determined using both a PCR-RFLP method and DNA sequence analysis. The most prevalent capsule biosynthesis gene among the isolates was capA (86.1%); a noticeable, however, rate of capD-positive isolates (38.6%) was found among the ovine isolates that had been associated primarily with the capsule type A in the past. Moreover, an unexpectedly high percentage of toxA-positive pneumonic isolates was noticed among small ruminants (93.2% and 85.7% in sheep and goats, respectively), indicating an important epidemiological role of toxigenic P. multocida for these species. Despite their great heterogeneity, certain ompA-genotypes were associated with specific host species, showing evidence of a host preference. The OmpA-based PCR-RFLP method developed proved to be a valuable tool in typing P. multocida strains.