Pneumonic infections associated with Mannheimia haemolytica in Nellore sheep: Isolation, molecular detection and virulence characterization

Abstract

Pneumonia is one of the major causes of morbidity and mortality in sheep worldwide. Mannheimia haemolytica, a bacterial pathogen involves majorly in acute respiratory form of pneumonia. The present study was carried out to isolate and molecularly characterize M. haemolytica from pneumonic lungs and nasal swabs of Nellore sheep showing clinical signs of respiratory illness. A total of 321 nasal swabs and 164 pneumonic lung samples were collected. Conventional culture methods when applied, yielded 54 isolates of M. haemolytica (33 from nasal swabs and 21 from lungs). Biochemical characterization when performed, the isolates were found to be catalase- and oxidase-positive, but negative for indole, urease, methyl red, Voges-Proskauer, and citrate utilization. PCR using species-specific primers (PHSSA and Rpt2) confirmed all isolates as M. haemolytica, while the virulence-associated lktA gene was consistently detected in all isolates. The sequences of the amplified PCR product of PHSSA showed 99-100% similarity with the published gene sequences in GenBank. Findings from the present study indicate that molecular diagnostics provide a sensitive and reliable tool for rapid identification of M. haemolytica in ovine pneumonia, and emphasize the importance of leukotoxin as a potential vaccine candidate in disease control.