Determination of Antimicrobial Susceptibility, Antimicrobial Resistance Genes and in vivo Testing of Antimicrobial Susceptibility of Avibacterium paragallinarum

Abstract

Avibacterium paragallinarum is the causative agent of infectious coryza, an acute upper respiratory disease in chickens. The aim of this study was to characterize the antimicrobial susceptibility, resistance genes and the in vivo testing of antimicrobial susceptibility in chickens. Eighteen A. paragallinarum isolated in Thailand were tested for antimicrobial susceptibility by broth microdilution method. A high prevalence of resistance MIC pattern to oxytetracycline, doxycycline, streptomycin, ciprofloxacin, erythromycin and sulfamethoxazole-trimethoprim was found. Thirteen isolates showed multiple antimicrobial drug resistance (66.7%). Resistance genes of tet(A), tet(B), tet(M), erm(A), erm(B), blaROB-1 and sul2 were found and the resistance genes of tet(A), tet(B) and tet(M) were revealed to be the highest percentage of resistance genes discovered (66.7%).The chickens were challenged with A. paragallinarum strains, which are sensitive and do not harbor any antimicrobial resistance genes against amoxicillin and doxycycline. Three days later, the challenged chickens were treated with amoxicillin and doxycycline. The treatment by sensitive antimicrobial drugs reduced the clinical signs in the challenged groups, but A. paragallinarum could be isolated from the infraorbital sinus 7 days after treatment. In conclusion, the sensitive antimicrobial agent could reduce the clinical signs of infectious coryza challenged by the sensitive antimicrobial and no harbor of antimicrobial resistance genes of A. paragallinarum.