Pasteurella] caballi infection not limited to horses - a closer look at taxon 42 of Bisgaard

AIM: To investigate if taxon 42 of Bisgaard isolated from pigs represents genuine Pasteurella] caballi, which was previously only isolated from horses. METHODS AND RESULTS: A total of 15 field isolates from horses and pigs from five different countries representing three continents were subjected to extended phenotypical characterization. Although minor differences were observed between taxon 42 and P.] caballi, these differences did not allow phenotypic separation. Ribotyping based on HindIII digestion showed five profiles based on nine band positions. One P.] caballi strain and two taxon 42 strains shared the same profile. Ribotyping using HpaII gave a higher diversity with nine profiles based on ten band positions. While no profiles were shared between the taxon 42 and P.] caballi strains, pattern analysis showed that two of the taxon 42 isolates were most similar (91% similarity) with a P.] caballi isolate. The 16S rRNA gene sequencing of one strain of taxon 42 and one strain of P.] caballi was performed and compared with the published sequence for the type strain of P.] caballi. The three strains showed nearly identical sequences with at least 99.8% similarity. DNA re-associations measured by the micro-well method were 79 and 77%, respectively between the type strain of P.] caballi and two strains of taxon 42 representing distinct ribotypes and confirmed that taxon 42 belongs to P.] caballi. CONCLUSION: The present investigation documents that P.] caballi can be isolated from clinical respiratory specimens from pigs and the recognized association with respiratory infections in horses and horse bite infection in humans. Strains classified as taxon 42 are P.] caballi isolated from pigs and for both pigs and horses, lesions mainly include the respiratory tract. SIGNIFICANCE AND IMPACT OF THE STUDY: The results will improve the diagnostics and progress studies of virulence and epidemiology of P.] caballi.