猪场大肠杆菌Ⅰ型整合子及其基因盒的分子流行病学研究

Molecular Epidemiology Studies on ClassⅠIntegron and Its Gene Cassette of Escherichia coli Strains Isolated from a Swine Farm

对某猪场大肠杆菌Ⅰ型整合子及其基因盒的分子流行病学进行了研究。结果表明:猪场大肠杆菌Ⅰ型整合子流行普遍,192株分离菌中105株携带Ⅰ型整合子,检出率达54.7%。共检出6种Ⅰ型整合子,它们以8种组合形式在猪场大肠杆菌中流行。猪群、饲养员及饲养环境分离菌株Ⅰ型整合子检出种类、检出率相近,但同耐药谱菌株Ⅰ型整合子携带无一致性。各种Ⅰ型整合子整合不同种类、不同数目的耐药基因盒,其中100%整合有氨基糖腺苷转移酶基因(aadA),77%整合有二氢叶酸还原酶基因(dhfr),仅少数整合有链丝菌素乙酰转移酶基因(sat)、β-内酰胺酶基因(bla)及红霉素酯酶基因(ereA)。Ⅰ型整合子携带菌株均表现多重耐药,其中100%耐受复方新诺明,90%耐受链霉素,75%耐受大观霉素。该猪场长期使用磺胺类、氨基糖苷类抗菌药物,尤其是将它们用作抗菌促长剂,造成了携带dhfr及aadA两种基因盒的Ⅰ型整合子在猪场大肠杆菌中广泛流行。

An investigation of class I integron and its gene cassette epidemiology in 192 Escherichia coli strains isolated from a swine farm was carried out by the methods of PCR, sequence, and restriction enzyme analysis. The result showed that one-hundred and five strains （54.7%） of E. coli harbored six types of class I integron in the form of eight combinations. All of E. coli strains from the pigs, the raisers, and the surroundings had similar prevalence of class I integron, but the strains with the same resistant patterns did not always carry the same type of class I integron. Each type of class I integron integrated different kinds and numbers of gene cassette. Among all the detected class I integrons, one-hundred percent carried aminoglycoside adenyltransferase （aadA）, seventy-seven percent carried dihydrofolate reductase （dhfr）, whereas only a small percentage carried one or two of the beta-lactamase （bla）, streptothricin acetyl-transferase （sat）, and erythromycin esterase （ereA） genes. All E. coli strains carried class I integrons were multi-resistant, especially resistant to compound sulfamethoxazole （ 100%）, streptomycin （90 %）, and spectinomycin （75%）. High prevalence of class I integrons carrying dhfr and aadA genes had occurred in E. coli strains because sulfonamides and aminoglycosides were used extensively, especially used as antibacterial growth promoter in this swine farm.