我国食品中大肠埃希菌O157耐药及PFGE分子分型特征分析

Antimicrobial susceptibilityanalysis and molecular typing by pulsed-field gel electrophoresis of Escherichia coli O157 isolated from food in China

目的了解我国食品中分离的110株大肠埃希菌O157的耐药及脉冲场凝胶电泳(PFGE)分子分型特征,完善我国食品中大肠埃希菌O157菌株特征的基础信息,为该菌的风险评估提供依据。方法使用琼脂稀释法对确认的110株大肠埃希菌O157进行药敏试验,完成耐药特征的分析。参照美国疾病预防控制中心PulseNet试验方法,对110株大肠埃希菌O157,运用XbaⅠ酶进行酶切并完成PFGE分析,利用BioNumerics软件对分离株的指纹图谱进行聚类分析。结果 1110株菌中,43株菌至少对一种抗生素有抗性。耐药率最多的前三种抗生素依次是四环素(30.0%,33/110),磺胺甲恶唑(29.1%,32/110),萘啶酸(26.4%,29/110);2一共有24个耐药谱,耐两种以上抗生素的菌株有34株,耐3种以上抗生素的多重耐药菌株有32株。最常见的三种耐药谱依次是SMX(6),AMP-NAL-SMX-SXT-TET(6),AMP-CHL-NAL-SMX-SXT-TET(4)/AMP-SMX-SXT-TET(4)/TET(4);3大肠埃希菌O157非H7(O157∶hund)对所测试的抗生素的耐药率明显高于大肠埃希菌O157∶H7(χ2=72.010 P<0.05)。其中37株携带了志贺毒素基因的大肠埃希菌O157∶H7仅对磺胺甲恶唑(2.7%,1/37)、萘碇酸(2.7%,1/37)有耐药,没有多重耐药菌株;4通过不同种类食品中大肠埃希菌O157菌株耐药率比较发现,从生猪肉、生禽肉中分离的菌株耐药率相对高于其他食品种类;5PFGE分子分型研究显示菌株具有基因多态性,且可以很好将大肠埃希菌O157非H7和大肠埃希菌O157∶H7菌株区分开。结论我国食品中分离的大肠埃希菌O157耐药现象严重。我们应加强养殖环节和零售环节食源性致病菌,特别是大肠埃希菌O157(包括产志贺毒素大肠埃希菌O157)菌株药敏特征的监测,探明食品与养殖环节菌株耐药的传播关系,并为国家制定科学的养殖业抗生素用药提供依据。

Objective To investigate the antimicrobial susceptibility and the pulse field gel electrophoresis （PFGE） patterns of 110 Escherichia coli O157 isolates from food in China, and to complete the characteristics of Escherichia coli O157 in food for the risk assessment. Methods Antimicrobial susceptibility of all confirmed Escherichia coli O157 isolates was determined by agar dilution method. DNA collected fromall strains was digested by Xba I according to the standard PFGE protocolof US CDC. The PFGE patterns were analyzed with BioNumerics software. Results Out of all the isolates, 43 strains were resistant to at least one antibiotic. The top three antibiotics were tetracycline （30.0% , 33/110） , sulfamethoxazole （29.1% , 32/ 110） , nalidixic acid （26. 4% , 29/ 110）. In total, 24 antimicrobial resistance profiles were identified. 34 isolates were resistant to more than two antibiotics and 32 resistant to more than three antibiotics. The dominant muhidrug resistant profiles were SMX （6） , AMP-NAL-SMX-SXT-TET （6） , AMP-CHL-NAL-SMX-SXT-TET （4） /AMP-SMX-SXT-TET （4） /TET （4）. The antibiotic resistance rate of E. coli O157 was significantly higher than E. coli O157：H7 （χ2 =72. 010 P 〈0. 05）. 37 E. coli O157：H7 isolates haboring shiga toxin genes only were resistant to sulfamethoxazole （ 2.7 % , 1/37 ） , nalidixicacid （2.7 % , 1/37 ） with no multi-drug resistant strains. Comparedby different food types, strains from raw pork and raw poultry had relatively higher resistance rates than other types of food. PFGE molecular typing completely separated E. coli O157： hund and E. coli O157：H7 strains. Conclusion The antimicrobial resistance of Escherichia coli O157 isolated from food in Chinawas serious. The antimicrobial susceptibility surveillance should be strengthened, especially for E. coli O157 （including STEC E. coli O157） isolates to explore the relationship and transmission of antibiotic resistance strains between farming areas and retail sectors and to provide a scientific basis to develop antibiotic medication in farming.