Molecular Detection and Antibiotic Susceptibility Profiling of <i>Mannheimia haemolytica</i> Isolates From Pneumonic Pasteurellosis Suspected Cases of Sheep in Northwestern Ethiopia

BACKGROUND: Mannheimia haemolytica is a major bacterial pathogen associated with respiratory diseases in domestic ruminants, resulting in devastating economic losses in the global food production industry. OBJECTIVES: This study aimed to isolate and assess the antibiotic resistance/sensitivity patterns of M. haemolytica associated with pneumonic pasteurellosis in sheep in the western Gojjam and Awi zones of Northwest Ethiopia. METHODS: One hundred and forty nasal swabs from sheep were collected using purposive sampling and subjected to standard bacteriological and polymerase chain reaction (PCR) assays. The antibiotic susceptibility of the isolates was assessed using Kirby-Bauer's disk diffusion method. RESULTS: The findings of this study revealed that M. haemolytica was the primarily identified agent of pneumonic pasteurellosis in sheep. Molecular analysis confirmed 23 M. haemolytica isolates. The antibiotic susceptibility test results showed sensitivity to oxytetracycline (78.3%), streptomycin (78.3%), chloramphenicol (87%), kanamycin (100%), gentamicin (100%) and ampicillin (100%), and resistance to erythromycin (100%). Four isolates showed multidrug resistance with a MAR index greater than 0.3. CONCLUSION: The findings underscore the potential role of M. haemolytica in causing pneumonic pasteurellosis in sheep in the region. In this study, due to resource limitations, further serotype determination and characterization of antigenic relationships among the isolates were not conducted. Molecular characterization of strains using high-throughput sequencing technologies is needed to elucidate the molecular mechanisms of pathogenesis and develop more effective, widely applicable vaccines and antimicrobial drugs.