动物源性和人源性的肠球菌对抗生素耐药性及ermB基因相关性研究

The study on drug resistance and ermB gene of Enterococci isolated from animal and human

目的了解大环内酯类耐药基因在人源和动物源性肠球菌之间水平转移的可能性。方法采用KB法和琼脂稀释法检测52株动物源性和55株儿科临床分离肠球菌对8种抗生素的敏感性；PCR检测肠球菌的ermB、mefA、terM、aac（6′）／aph（2″）基因以及Tn1545的整合酶沈基因；PCR扩增联合测序对比人源性和动物源性ermB等位基因的同源性；接合实验研究ermB基因在不同种属、不同来源的肠球菌之间水平转移。结果两种来源肠球菌对红霉素的耐药率高达80％以上；ermB是肠球菌对红霉素耐药的主要基因，在人源性和动物源性肠球菌的检出率分别为61，82％（34／55）和53．85％（28／52）；已测序菌株中53．0％的北京临床分离株与69．5％的动物分离株携带同一ermB等位基因EF525477；通过接合实验，ermB基因可以在不同来源、不同种属分离株之间进行传递。结论动物源性和人源性肠球菌对红霉素和四环素都有高耐药率；滤膜实验证实ermB基因在体外条件下可以在动物源性肠球菌和人源性肠球菌之间传递，但传递频率比较低。动物源性和人源性肠球菌及不同种属的肠球菌有相同ermB等位基因，提示其ermB耐药基因在动物源性和人源性肠球菌水平传递存在的可能性。

Objective To obtain better insights into transmission dynamics of maerolide resistance genes between human and animal Enterococcus strains. Methods The antimicrobial susceptibility to 8 antibiotics of 52 Enterococci isolated from animal and 55 Enterococci isolated from human was determined. PCR was used to detect the macrolide resistance genes ermB and mefA, tetracycline resistance genes tetM, and the integrase gene int of Tn1545 of the total 107 strains. Forty-nine ermB positive strains were chosen to be sequenced. Filter mating experiments were taken. Results The resistance rate to erythromycin were 89.09% and 80.77% for isolates from human and animal; and resistance rate to tetracycline were 80.00% and 67.31% for isolates from human and animal, respectively. All isolated Enterococci strains were found sensitive to vancomycin ermB was detected in 61.82% human Enterococci and 53.85% porcine ones. Identical ermB gene sequences were found in animal and human Enterococci. Transfer of the ermB gene from porcine E. faecalis to human E. feacalis was successful, and the transfer frequency is 1.2× 10^-5. Conclusion Enterococci have a high resistance rate to erythromycin and some other antibiotics, especially in pediatric isolates; but still very sensitive to glycopeptide, ermB was the predominant genes for macrolide and tetracycline. Identical ermB gene sequences were present in animal and human Enterococci and that transfer of the ermB gene from porcine E. faecalis to human E. faecalis and vice versa is possible, but probably occurs at a low frequency.