Quinolone resistance in Escherichia coli and Salmonella spp. isolates from diseased chickens during 1993-2008 in China

A total of 363 Escherichia coli and 224 Salmonella spp. were isolated from diseased chickens during 1993-2008 in China. The susceptibility to eight quinolones and prevalence of plasmid-mediated quinolone resistance (PMQR) determinants was investigated in these isolates. Among the E. coli isolates obtained during 1993-1999, 65.2% were resistant to nalidixic acid, while more than 50% of the E. coli isolates collected during 2000-2008 were resistant to 7 quinolones. All 101 Salmonella spp. isolates obtained during 1993-1999 were susceptible to quinolones, while more than 50% of the Salmonellaspp. isolates collected during 2000-2008 were resistant to only nalidixic acid (82.9%). Among the 363 E. coli isolates, 4 (1.1%) were positive for aac(6′)-Ib-cr, 3 (0.8%) for qepAand 1 (0.3%) for qnrB10. No PMQR gene was identified in 224 Salmonella spp. isolates. The resistance of E. coli and Salmonella spp. to quinolones has been increasing in the past twenty years and the resistance of Salmonella spp. was much lower than that of E. coli, although they were separated in the same period. There is a rising trend of avian isolates harboring PMQR genes in China.   Key words: Quinolone resistance, qnr; aac(6′)-Ib-cr; qepA, chicken.