Characteristics of Fluoroquinolone-Resistant of Avian Pathogenic Escherichia coli Isolates in China

摘要

A total of 121 Avian Pathogenic Escherichia coli (APEC) isolates recovered from diagnosed cases of avian colibacillosis from China during 2009 and 2011 were serotyped and examined for susceptibility to nalidixic acid and 6 fluoroquinolones. About 23 different serotypes were determined by agglutination using antisera and 078 (28/121), O143 (21/121) and O2 (15/121) were predominant serotypes. APEC isolates displayed resistance to nalidixic acid (95.9%), norfloxacin (95.0%), ciprofloxacin (94.2%), enrofloxacin (86.8%), levofloxacin (75.2%), lomefloxacin (63.6%) and ofoxacin (61.2%), respectively. Single gyrA changes (mainly Ser 83 to Leu) correlated with nalidixic acid MICs ≥32 μg mL-1. The Asp87 changes (mainly Asp87 to Asn) in gyrA were associated with higher ciprofloxacin MICs. ParC alterations comprised amino acid changes Ser 80 to Ile, Ser 80 to Arg, Glu84 to Gly, Glu84 to Lys. The fluoroquinolone-resistant strains for which nalidixic acid MICs were >256 μg mL-1 had both gyrA sand parC QRDR point mutations. The fluoroquinolone-resistant isolates had common point mutations in gyrA (Ser 83 to Leu, Asp87 to Asn) and parC (Ser80 to Ile). These strains for which ciprofloxacin MICs were >8 μg mL-1 had double gyrA mutations, accompanying with ParC alterations. Seven recent isolates carried qnrS gene and three carried aac(6')-Ib-cr gene. This suggests that the widespread mutations at position 83, 87 of gyrA and position 80 of parC were crucial for resistance to fluoroquinolone and showed significant relation to the high-level fluoroquinolone resistance in APEC.