Molecular evaluation of Pasteurella multocida in livestock, characterization of virulence genes, and pathogenic potential of the retrieved isolates in Iran.

Abstract

Background: Pasteurellosis remains one of the most economically important diseases in Asia. Aims: The present study aimed to isolate Pasteurella multocida from cattle, sheep, and goats, perform molecular identification and capsular typing, evaluate the presence of selected virulence genes, examine pathogenicity using minimum infectious dose (MID) assay, and determine antimicrobial susceptibility.

Methods: The study was performed on 600 samples collected from ailing sheep, goats and cattle. Identification of P. multocida isolates using standard biochemical tests and kmt1 gene amplification, molecular capsular typing, and identification of 14 virulence genes were determined by PCR method. The pathogenicity of each isolate was assessed by injecting a minimum infectious dose (9 × 10⁶ CFU/ml) of the isolate suspension into Balb/C mice. The susceptibility of isolates for 9 antibiotics was investigated using the disk diffusion method according to CLSI criteria.

Results: A total number of 80 isolates were identified as P. multocida from 38 sheep, 28 goats and 14 cattle. Type A was the most prevalent capsular type (62.5%), while capsular type B was not detected. Among the virulence genes, exbD (97.5%), plpB (90%), pmHAS (82.5%), exbB (80%), and toxA (80%) were the most frequently observed. hsf2 was the only adhesion gene in cattle. MID results showed that 62 isolates infected mice.

Conclusion: Our results indicate that the presence of a greater number of virulence factors does not correlate with increased pathogenicity. Pathogenesis of toxA gene is mostly dependent on the host and this gene alone cannot cause disease in sheep, goats and cattle. Among the studied antibiotics, enrofloxacin was preferred for the treatment of pasteurellosis.