Abstract
This study was conducted in West Azerbaijan province, Iran (37°27'18.022" N, 45°0'0" E) to investigate the genotyping and phylogenetic characterization of Mannheimia haemolytica in cattle and buffaloes from November 2022 to January 2024. Mannheimia haemolytica is a bacterium known to cause pasteurellosis pneumonia, a respiratory disease in ruminants, such as cattle and sheep. This is one of the main causes of economic losses in the feedlot industry. In addition to the deaths, treatment costs are also significant. The lung and nasal swab samples were collected from 378 cattle and buffaloes. The M. haemolytica was detected in 32 (8.46%) of the samples, with a notably higher isolation rate from lung tissue (56.25%; n = 18) compared to the nasal swabs (43.75%; n = 14). Interestingly, the study also revealed a seasonal pattern, with the highest isolation rates observed during January, February, and March. Multi-locus sequence typing demonstrated that all isolates belonged to sequence type 1 (ST1) within clonal complex 28. This finding is consistent with the global prevalence of ST1 in bovine isolates, indicating widespread distribution. Phylogenetic analysis revealed a strong correlation between ST1 and STs 30 and 54, highlighting the prevalence of ST1 in M. haemolytica among ruminants in West Azerbaijan, Iran. Further research is needed to investigate its potential for causing disease and its transmission pattern.