To study the distribution and molecular characterization of integron-gene cassettes in multidrug-resistant Escherichia coli isolates from food-producing animals in Sichuan province, multiplex PCR was used to detect 3 different classes of integrase genes in 327 isolates. The sequences of the gene cassettes in integron-positive strains were analyzed by PCR-sequencing. The results of multiplex PCR indicated that 294 (89. 91%) of 327 isolates harbored intl I , and neither intl II nor intl I Ⅲ was detected in those isolates. 800-3 000 bp amplicons of gene cassettes were yielded in 67 of 81 intl I -positive strains choosed randomly. The main cassettes were those encoding aminoglycoside adenyltransferase A (aadA) and dihydrofolate reductase (dfrA, dhfrI). The most prevalent array of gene cassettes was dfrA17+aadA5. aacA4+catB3+dfrA1 and aadA22 were discoveried in two strains, respectively. aadA22 encoding resistance to aminoglycosides was firstly reported in avian E. Coli from Sichuan province. Intl I was extensively existed in E. Coli isolates. Although there was not a correlation between resistant patterns and integron-gene cassettes in the study, identical gene cassette fragments were found in different strains, suggesting horizontal transfer among different strains may have occurred by integron.%为研究分离自四川省食品动物源大肠杆菌多重耐药菌株整合子-基因盒分布及分子特征,采用多重PCR方法检测327株多重耐药菌株中I、Ⅱ、Ⅲ型整合酶基因,用PCR-测序法对整合子阳性菌进行基因盒序列分析.结果表明327株Escherichia coli中294株(89.91%)检出有I型整合子,未检出Ⅱ、Ⅲ型整合子.在随机选取的81株l型整合子阳性菌中,67株(82.72%)能扩增出800～3000 bp的耐药基因盒插入区.基因盒以编码对甲氧磺胺嘧啶类和氨基糖苷类药物耐药的dfrA、dhfrI和aadA基因家族为主,尤其以dfrA17+aadA5为优势基因盒.分别在2株菌中检出aacA4+catB3+dfrA1和aadA22基因盒.aadA22是四川分离菌株中首次报道,介导氨基糖苷类耐药.结果表明I型整合子普遍存在于大肠杆菌临床菌株中.尽管菌株携带的整合子-基因盒与其多重耐药谱间不存在对应关系,但不同来源菌株中检测出相同的耐药基因盒片段,说明了通过整合机制耐药基因可在不同菌株问水平传递.
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