Ornithobacterium rhinotracheale (ORT), a species of bacteria, is known to be associated with respiratory
disease, growth retardation, mortality and decreased egg production. The aim of the present study was to
determine seroprevalence of the infection and to identify the microorganism by bacteriological and molecular
methods. In this study, 460 serum samples and also 290 tracheal swabs were collected from 29 broiler
chicken flocks in slaughter houses. Serological results showed that 24 out of 460 (5.12%) serum samples
related to 5 flocks were positive for ORT by ELISA test. ORT was isolated from tracheal swabs of 3 flocks
(1.03% out of 290 tracheal swabs) by culture and confirmed as ORT by specific primers in PCR method.
Statistically, there was no significant difference between the rate of isolation and ORT serum titers (P>0.05).
Antibiotic sensitivity test using standard disk diffusion technique was performed with 13 antibiotics. All the
isolates were resistant (100%) to erythromycin, tetracycline, oxytetracyclin, enrofloxacin, ciprofloxacin,
flumequin, lincospectin, furazolidon, and 100% of them were found to be susceptible to ceftriaxon and
tiamulin, but 2 isolates (66.7%) were moderately sensitive to tylosin and amoxicillin and sensitive to
florfenicol. This study is the first report of the prevalence of ORT, bacterial isolation and molecular method
in broiler chickens after broiler breeder vaccination in Guilan province.