Isolation, identification, and monitoring of antibiotic resistance in Pasteurella multocida and Mannheimia haemolytica isolated from sheep in East Azerbaijan province, Iran

The present study was carried out in order to isolate, identify, and assess the antimicrobial susceptibility of the causative agent(s) of pneumonic pasteurellosis in sheep in East Azerbaijan province, northwest of Iran. Pneumonia was detected in 320 cases, and the affected lungs were sampled in the slaughterhouse. The samples were investigated bacteriologically for the isolation of two microorganisms from the Pasteurellaceae family. Pasteurella multocida was isolated from six (1.87%) samples, while none of the lung tissues were positive for Mannheimia haemolytica. After the isolation and detection of microorganisms via cultural and morphological tests, the bacteria were identified on the basis of biochemical criteria and polymerase chain reaction (PCR) technique. Antimicrobial susceptibility testing was performed on all P. multocida isolates, using broth microdilution method. Evaluation of the minimum inhibitory concentration (MIC) of eight antimicrobial agents against the tested isolates showed that all the organisms were resistant to amoxicillin and relatively susceptible to ceftiofur. In conclusion, P. multocida was introduced as the main cause of ovine pneumonic pasteurellosis in the studied district, and the outbreak frequency significantly varied in different seasons of the year (P<0.05).