食品动物源大肠杆菌多重耐药菌株整合子-基因盒的分子特征

Molecular Characterization of Integron-gene Cassettes in Multidrug-resistant Escherichia coli Isolates from Food-producing Animals

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Ⅰ型整合子阳性菌中,67株(82.72%)能扩增出800～3 000bp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间水平传递。

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 intIⅠ,and neither intIⅡ nor intIⅢ was detected in those isolates.800-3 000 bp amplicons of gene cassettes were yielded in 67 of 81 intIⅠ-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.IntIⅠwas 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.