Isolation, characterization, and genotyping of Ornithobacterium rhinotracheale isolated from broiler and broiler breeder flocks in Mazandaran province, Northern Iran.

Background: Ornithobacterium rhinotracheale (ORT) is one of the most important pathogenic bacteria which cause significant economic losses in poultry breeder countries every year. Aims: The present study was conducted to isolate and investigate the ORT isolates' biochemical, antibiotic resistance, and genotypic characteristics of in industrial poultry flocks with respiratory signs in northern Iran.

Methods: After sampling from 60 different flocks and cultivation of the samples on a selective medium, suspected colonies were subjected to biochemical and molecular identification of ORT. Then, confirmed isolates were aimed to antibiotic resistance assay, hemagglutination test, detection of pOR1 plasmid, and DNA fingerprinting to survey the variability of the isolates.

Results: A total of 13 isolates, including seven isolates from broiler flocks (19.44%) and six isolates from broiler breeder flocks (25%) were obtained. Almost all isolates showed similar results in terms of basically important biochemical tests. The most resistance rates among all ORT isolates were obtained for ampicillin, erythromycin, ceftriaxone, and penicillin (100%). The majority of ORT isolates were susceptible to furazolidone. The pOR1 plasmid was detected in only two isolates, and analysis of the DNA fingerprinting phylogenetic tree showed four specific genotypic clusters.

Conclusion: According to the results, the isolates showed different antibiotic resistance profiles, and most of the strains proved multiresistant. This can indicate the circulation of various multi-drug resistant strains among poultry farms in northern Iran. Isolates from broilers and broiler breeders were grouped into different clusters by genotyping.