Isolation, Molecular Characterization and Antibiotic Susceptibility Pattern of Pasteurella multocida Isolated from Cattle and Buffalo from Ahwaz, Iran

Pasteurella multocida is a gram-negative, opportunistic pathogen and the common inhabitant of the upper respiratory tract of domesticated and wild animal species. It is a causative agent of numerous economically important diseases worldwide, such as enzootic bronchopneumonia in ruminants and haemorrhagic septicemia in cattle and buffalo. The present study was undertaken to determine the prevalence of P. multocida carriers, PCR-serogrouping and antibiotic susceptibility status of isolates detected in cattle and buffalo in Ahvaz, Iran. Nasopharyngeal and nasal swabs were collected from 227 cattle and 174 buffaloes. The swabs were streaked on MacConkey and sheep blood agar and incubated for 24-48 h at 37 °C. The presumptive P. multocida colonies were identified based on standard biochemical testing and further confirmed by PCR. A multiplex PCR was used to determine the five pathogen serogroups (i.e., A, B, D, E, and F). Antimicrobial susceptibility of P. multocida isolates was determined using the Kirby–Bauer disc diffusion method on Mueller-Hinton agar supplemented with 5% sheep blood. Out of 401 tested samples, P. multocida was recovered from 10/227 (4.4%) and 12/174 (6.89%) cattle and buffaloes, respectively. Fifteen isolates (68.19%) belonged to serogroup A, 5 (22.72%) to serogroup D, and 2 (9.09%) isolates were untypeable. No isolate belonged to B, E, and F serogroups. All P. multocida isolates were sensitive to nitrofurantoin, florfenicol, ciprofloxacin, enrofloxacin, trimethoprim-sulfamethoxazole, oxytetracycline, and ceftriaxone. The most common finding was resistance to tylosin (90.9%), followed by resistance to oxacillin (54.54%).