Riemerella anatipestifer and Ornithobacterium rhinotracheale are among the several causative agents of respiratory tract infections that are causing heavy economic losses in the poultry industry worldwide. At the same time, the emergence of multi-drug resistance is becoming one of the major medical and veterinary concerns and the overuse of antibiotics in veterinary medicine has contributed to the selection of resistant pathogens.
Antimicrobial susceptibility of 100 R. anatipestifer and 38 O. rhinotracheale strains isolated from various avian hosts were determined by Kirby-Bauer disk diffusion method. Most R. anatipestifer strains were susceptible to florfenicol, penicillin, spectinomycin and sulphamethoxazole trimethoprim and resistant to flumequine, tetracycline, doxycycline and erythromycin, while a majority of O. rhinotracheale strains were resistant to nalidixic acid, sulphamethoxazole trimethoprim and gentamicin, and were susceptible to ampicillin, chloramphenicol spectinomycin and tilmicosin.
Multi-resistant strains were subjected to plasmid isolation. No plasmid was isolated from O. rhinotracheale strains. On the other hand, 31 out of the 33 examined R. anatipestifer strains yielded ~3000-20000 bp sized plasmids.