奶源大肠杆菌的分离鉴定及耐药性分析

Isolation and identification of Escherichia coli in milk and its drug resistance analysis

目的了解原料乳和乳房炎奶样中大肠杆菌的污染情况及菌株耐药性。方法通过选择培养和聚合酶链式反应方法对2个奶牛场采集到的206份奶样(129份乳房炎牛奶样品和77份原料乳样品)进行大肠杆菌的分离鉴定,采用药敏纸片法对分离株进行25种常用抗生素耐药特征检测。结果206份奶样中大肠杆菌的污染率为8.3%(17/206),其中乳房炎和原料乳样品的污染率分别为7.0%(9/129)和10.4%(8/77)。从17份污染的样本中共分离到34株大肠杆菌,其中乳房炎奶样分离到18株,原料乳分离到16株。药敏结果显示,奶样分离株对氨苄西林耐药最为普遍(44.1%,15/34),对头孢类抗生素也有较强耐药性[如头孢唑啉和头孢噻吩(20.6%,7/34)]。最常见的耐药谱为AMP(11.8%,4/34),AMP-CXM-CFZ-KF-F和AMP-CXM-CFZ-CTX-PRLCRO-KF(5.9%,2/34)。此外,A,B奶牛场分离株的耐药率(P=0.007)和耐药谱总体差异显著(P=0.043)。结论奶样中存在大肠杆菌的污染情况,菌株普遍对氨苄西林和头孢类抗生素耐药且部分对非兽用抗生素也有一定的耐药性。因此,为避免耐药大肠杆菌对人类,尤其是抵抗力较弱的老年人和婴幼儿的感染和中毒,除应加强对奶源地的管理外,还需防止抗生素的滥用。

Objective To investigate the contamination and drug resistance of Escherichia coli(E.coli)in raw milk and mastitis milk samples.Methods The E.coli strains contained in 206 milk samples(129 samples of mastitis milk and 77 samples of raw milk)from 2 dairy farms were isolated and identified by selective culture and PCR.The drug-sensitive paper method was used to detect the resistance of 25 commonly used antibiotics to isolates.Results The contamination rate of E.coli in 206 milk samples was 8.3%(17/206),and the contamination rates of mastitis and raw milk samples were 7.0%(9/129)and 10.4%(8/77),respectively.A total of 34 E.coli strains were isolated from 17 contaminated samples,including 18 isolated from mastitis and 16 from raw milk samples.Drug susceptibility results showed that milk sample isolates were the most commonly resistant to ampicillin(44.1%,15/34)and showed the higher drug resistance cephalosporin antibiotics[such as cefazolin and cefalotin(20.6%,7/34)].The most common antimicrobial resistance profiles were AMP(11.8%,4/34),AMP-CXM-CFZ-KF-F and AMP-CXM-CFZ-CTX-PRL-CRO-KF(5.9%,2/34).Moreover,the overall differences in drug susceptibility(P=0.007)and antimicrobial resistance profiles(P=0.043)between A and B dairy isolates were significant.Conclusion The contamination of E.coli is existed in milk samples,and the strains are generally resistant to ampicillin and cephalosporin,and some are also resistant to non-veterinary antibiotics.Therefore,to avoid the occurrence of infection and poisoning of resistant E.coli to humans,especially the elderly and infants with weak resistance,it is suggested not only to strengthen the management of the milk source but also to prevent the abuse of antibiotics.