Isolation and Molecular Identification of Avibacterium paragallinarum Isolated from Commercial Layer and Backyard Chickens in Iran

Avibacterium paragallinarum causes infectious coryza that is an important disease of chickens associated with an acute upper respiratory infection, growth retardation, marked drop in egg production, reduced hatchability, and increased number of culls. Infectious coryza has been reported from all around the world including Iran where chickens are raised.

This study was conducted to isolate Avibacterium paragallinarum from the suspected cases of infectious coryza in the backyard and commercial layer chickens in three provinces of Tehran, Alborz, and Qazvin in Iran, to characterize the isolates by molecular methods and to determine their antimicrobial susceptibility profile.

Swab samples from eye secretions and mouth cavity were provided from five commercial laying farms (25 samples) and backyard chickens (20 samples) suspected of infectious coryza in Tehran, Alborz, and Qazvin provinces of Iran. Standard bacteriological and biochemical procedures were performed for the isolation and identification of Av. paragallinarum. The antimicrobial susceptibility of the recovered isolates was determined by the agar disk diffusion method. HPG-2 PCR was used to confirm Av. paragallinarum using the specific primers of N1 and R1, resulting in a 500 bp amplicon. PCR-amplified hmtp210 gene with the amplicon size of 1.6 kb was subjected to sequencing with the standard Sanger sequencing method and phylogenetically analyzed.

Three Av. paragallinarum isolates were obtained from all the cultured samples. Antimicrobial sensi-tivity test revealed that all three isolates were resistant to amoxicillin, oxytetracycline, streptomycin, ampicillin, and colistin while they were susceptible to cephalexin, ceftriaxone, florfenicol, gentamicin, linco-spectin, neomycin, and doxycycline. In phylogenetic analysis, two different genotypes of Av. paragallinarum were found.

In this study, Av. paragallinarum isolates recovered from layer flocks were genotypically closely related to the strains from serovar C while the isolate recovered from backyard chickens was closely related to serovar B strains. Our results showed that the antimicrobial susceptibility is highly variable among the Av. para-gallinarum isolates compared to previous studies. Future studies are required to develop better immunogenic strategies and eventually novel vaccine candidates to control the disease and reduce the risk of infection with multi-drug resistant Av. paragallinarum isolates.