零售鸡肉中环丙沙星与头孢噻肟双耐药大肠杆菌的检测与遗传特征分析

Prevalence and characterization of cefotaxime and ciprofloxacin co-resistant Escherichia coli isolates in retail chicken carcasses

目的评估我国社区零售鸡肉中多重耐药大肠杆菌的污染危害。方法2011年4月至12月间,从陕西、广东、内蒙古采集新鲜整鸡样品207个,对环丙沙星与头孢噻肟双耐药大肠杆菌进行分离、遗传分型和药敏分析,并应用PCR扩增和测序方法对喹诺酮和三代头孢耐药机制进行分析。结果 35.7%(73/207)的零售整鸡样品中检出环丙沙星与头孢噻肟双耐药大肠杆菌,以系统发生A群为主(61.6%,45/73),所有菌株均为多重耐药株,优势耐药谱型为AMP-CAZ-CTX-CIP-CHL-SXTTET(n=34)和AMP-CAZ-CTX-CIP-CHL-GEN-SXT-TET(n=24),所有菌株的拓扑异构酶喹诺酮耐药决定区中均有点突变,多数菌株的突变数量为3个(n=56)或4个(n=12),从50个菌株中检出质粒介导喹诺酮耐药机制,包括oqxAB(n=48)、aac(6')-Ib-cr(n=5)、qnrS1(n=5)和qnrS2(n=3)。从72株大肠杆菌中共检出6个blaCTX-M型,其中blaCTX-M-55(n=62)为优势型。结论本研究检测的社区零售整鸡是环丙沙星与头孢噻肟双耐药大肠杆菌的重要储存库。

Objective To investigate the prevalence and characteristics of cefotaxime and ciprofloxacin co-resistant Escherichia coli isolates in retail chicken samples and provide baseline data for the risk assessment and evaluation of new control measures of multi-drug resistant E. coli isolates in retail chicken products. Methods Whole chicken carcasses （n = 207） were collected from Shanxi （ n = 91 ）, Guangdong （ n = 63 ） and Inner Mongolia （n = 53） from April to December in 2011, cefotaxime and ciprofloxacin co- resistant E. coli isolates were recovered and subjected to phylogenetic group typing and antimicrobial susceptibility testing. All isolates were further characterized by screening for beta-lactamase genes, quinolone resistance determinants by PCR and followed by DNA sequence analysis. Results Cefotaxime and ciprofloxacin co-resistant E. coli isolates were recovered in 35.7% （73/207） of retail chicken carcasses. E. coli isolates of phylogenetic group A were dominant （61.6%, 45/73 ） and all the isolates showed multidrug resistant profiles. The dominant resistant profiles were AMP-CAZ-CTX-CIP- CHL-SXT-TET （n = 34） and AMP-CAZ-CTX-CIP-CHL-GEN-SXT-TET （ n = 24）. Pointmutations in quinolone resistance determination regions of topoisomerases were identified in all the isolates and most of the isolates accumulated three （n = 56） or four （n = 12） point mutations. Plasmid mediated quinolone resistant determinants were identified in 50 isolates, including oqxAB （ n = 48 ）, aac （ 6＇）-Ib-cr （ n = 5 ）, qnrS1 （ n = 5 ） and qnrS2 （n = 3）. Six subtypes of blaCTX-M were identified in 72 E. coli isolates and blaCTX- M-55 （n = 62） was dominant. Conclusion Retail chicken could serve as an important reservoir of cefotaxime and ciprofloxacin co-resistant E. coli isolates.