Isolation, Molecular Detection and Antimicrobial Sensitivity Profile of Pasteurella multocida Isolates from Cattle Affected with Haemorrhagic Septicaemia in the Puducherry Region

Abstract

Aims: To isolate, molecularly detect and evaluate the antimicrobial sensitivity profile of Pasteurella multocida from cattle clinically suspected of haemorrhagic septicaemia in the Puducherry region, and to assess the diagnostic value of blood smear examination and real-time PCR. Study design: A cross-sectional observational study involving clinically suspected cattle was conducted to compare conventional and molecular diagnostic findings and to determine antimicrobial sensitivity patterns of culture-confirmed isolates. Place and Duration of Study: Large Animal Medicine Unit, Veterinary Clinical Complex, Rajiv Gandhi Institute of Veterinary Education and Research (RIVER), Puducherry, India. The study was carried out over a period of twelve months. Methodology: Sixty-three unvaccinated cattle showing clinical signs suggestive of haemorrhagic septicaemia were examined. Blood smears were stained with Leishman stain for detection of bipolar organisms. Whole blood samples were subjected to real-time PCR targeting the KMT1 gene for confirmation of P. multocida. Ten qPCR-positive samples were cultured on Sheep Blood Agar for bacterial isolation. Antimicrobial sensitivity was assessed using the Kirby–Bauer disc diffusion method with commonly used therapeutic agents. Results: Out of sixty-three suspected cases, twenty-one animals (33.33%) were positive for P. multocida by both blood smear examination and real-time PCR. All smear-positive samples showed amplification in qPCR with Cycle Threshold values ranging from 12 to 29. Culture of ten qPCR-positive samples yielded non-haemolytic, dew-drop–like colonies consistent with P. multocida. Antimicrobial sensitivity testing revealed 100% sensitivity to Enrofloxacin and Gentamicin, followed by Cefquinome (90%), Ceftiofur (80%) and Co-trimoxazole (50%), whereas complete resistance was observed to Penicillin G and Oxytetracycline. Conclusion: Real-time PCR proved to be the most sensitive diagnostic tool for rapid confirmation of haemorrhagic septicaemia. The antimicrobial profile indicates high efficacy of fluoroquinolones, aminoglycosides and cephalosporins against P. multocida, while resistance to Penicillin G and Oxytetracycline highlights the need for rational therapeutic selection in affected cattle.