Quantitative real-time PCR study of the expression and regulation of the tetracycline resistance gene in Riemerella anatipestifer.

Riemerella anatipestifer (RA) is one of the most important pathogens of 1- to 8-wk-old ducklings that severely affects the development of the duck industry in China. Every year, antibiotic medicines including tetracycline and doxycycline are used in the duck industry. Few reports compare the expression of multidrug-resistant genes in RA before and after addition of chemical drugs.

Antibiotic susceptibility of Riemerella anatipestifer field isolates.

Kirby-Bauer tests were used to analyze the antibiotic resistance of 224 isolates of Riemerella anatipestifer isolated between 1998 and 2005. Among the 36 antibiotics tested, 50% of the analyzed isolates were resistant to ampicillin, ceftazidime, aztreonam, cefazolin, cefepime, cefuroxime, oxacillin, penicillin G, rifampin, and trimethoprim/sulfamethoxazole. Higher levels of resistance were detected for aztreonam, cefepime, oxacillin, penicillin G, ceftazidime, and trimethoprim/sulfamethoxazole (87.