Identification, capsular typing and virulence factors of Pasteurella multocida isolates from Merino lambs in Extremadura (Southwestern Spain)

This report describes the prevalence, capsular type and virulence factors of Pasteurella multocida isolated from the respiratory tracts of healthy and diseased lambs. For this study, five hundred and ninety-eight fattening lambs from different feedlots of the community of Extremadura were analysed. Isolation and identification of P. multocida were performed using conventional bacteriological and biochemical techniques, while confirmation of P. multocida identification, capsular type and virulence factors was done using the polymerase chain reaction technique (PCR). Of 598 studied lambs (410 clinically healthy and 188 diseased sheep), P. multocida was isolated from 37 animals (6.2%), with prevalence rates of 0.49% (2/410) in healthy lambs and 18.62% (35/188) in diseased lambs confirming a close relationship between the presence of bacteria and disease. Capsular typing of P. multocida isolates demonstrated two capsular types: A (15) and D (22), with general prevalence rates of 40.5% and 59.5%, respectively, and with the exclusive presence of type D in healthy animals (100%) and types D and A among diseased animals (42.9% and 57.1%, respectively). Among four virulence genes investigated (pfhA, hgbB, tbpA and toxA), we found a remarkable high prevalence of tbpA (100%) (37/37) genes in P. multocida; toxA was only detected in some diseased lambs (11/37), while the rest of the studied genes were not detected. The high prevalence of toxA among isolates from diseased animals may imply an important role of this gene in the virulence of P. multocida isolates in sheep, especially in diseased lambs.