鱼源嗜水气单胞菌多重耐药菌株整合子的分子特征

为研究嗜水气单胞菌多重耐药菌株整合子-基因盒分布及分子特征, 首先采用K-B纸片扩散法检测28株鱼源嗜水气单胞菌对18种抗生素的耐药性, 然后利用PCR方法检测菌株中Ⅰ、Ⅱ、Ⅲ型整合酶基因并对其携带基因盒序列进行分析。结果表明, 分离到的鱼源嗜水气单胞菌呈多重耐药性, 对b-内酰胺类、大环内酯类、氯霉素类和四环素类药物的耐药率超过60%, 而对氟喹诺酮类药物较敏感, 且菌株间耐药谱差异较大。53.57%的菌株Ⅰ类整合子阳性, 21.43%的菌株Ⅱ类整合子阳性, 整合子阳性菌株对多种药物的耐药率均高于阴性株, 且Ⅰ类整合子阳性株多重耐药率明显高于Ⅱ类整合子阳性株, 表明整合子系统在嗜水气单胞菌多重耐药性中发挥重要作用。Ⅰ类整合子基因盒以aadA、dfrA、catB家族为主, 分别介导氨基糖苷类、甲氧磺胺嘧啶类和氯霉素类药物耐药; 基因盒的排列以aadA2+dfrA12类型为主。此外, Ⅰ类整合子阳性的嗜水气单胞菌多重耐药性在不同个体间也存在较大差异, 提示多重耐药菌株的耐药表型与基因盒的类型无直接相关性。

Molecular characterization of integron-gene cassettes in multi-drug resistant Aeromonas hydrophila from fish

The aim of this study was to explore the distribution and composition of integron-gene cassettes in multi-drug resistant (MDR) Aeromonas hydrophila, and to understand the relationship between integrons and MDR, so that we can accurately evaluate the status of integron-gene cassette systems in the MDR mechanisms of A. hydrophila. To determine the distribution and molecular characterization of integron-gene cassettes in 28 multi-drug resistant A. hydrophila isolates from fish, the K-B disk diffusion method was employed to determine the antimicrobial susceptibility of the isolates to 18 different antibiotics. PCR amplification was then performed to detect class I, II, and III integrons and their gene cassettes in A. hydrophila. The results indicate that A. hydrophila isolated from fish exhibited multi-drug resistance, with an antibiotic resistance rate of more than 60% to b-lactams, macrolides, chloramphenicols, and tetracycline antibiotics, while it was more sensitive to fluoroquinolones. The drug resistant spectrum also differed greatly among the isolates. The PCR amplification results showed that out of 28 isolates, 15 (53.57%) harbored int1 I and 6 (21.43%) harbored int1 II, however, no int1 III was detected in the isolates. Combined with the antimicrobial susceptibility results, the drug resistant rate of the integron positive strains was higher than that of the integron negative ones. In addition, class I integron positive strains exhibited a higher multi-drug resistant rate than those harboring class II integrons, which indicates that the integron-gene cassette system plays an important role in the occurrence of multi-drug resistance in A. hydrophila. The main cassettes were those encoding aminoglycoside adenyltransferase A (aadA), dihydrofolatereductase A (dfrA), and chloramphenicol acetyltransferase B (catB). The most prevalent gene cassette array was aadA2+dfrA12. In addition, there was an obvious difference in MDR among individuals containing class I integrons, hinting that no direct relationship exists between the MDR phenotype and gene cassettes in the A. hydrophila isolates. These findings suggest that the transfer of antibiotic resistance genes can occur through integron-gene cassettes among A. hydrophila.