红霉素耐药肠球菌的质粒接合试验

目的：研究儿童临床分离的30株肠球菌,红霉素耐药性在同属同种、同属异种和异属细菌之间的传递。方法：使用临床实验室标准化研究所（CLSI）推荐的琼脂稀释法筛选30株耐红霉素的肠球菌,通过滤膜接合法进行质粒接合转移试验,采用PCR检测供体菌、受体菌和接合子ermB基因和转座子Tn1545、Tn917。结果：13株粪肠球供体菌通过质粒接合转移试验后得到13株接合子,红霉素最小抑菌浓度（MIC）≥512μg／ml,除原供体菌1株粪肠球菌阴性外,其余的12株接合子全部携带ermB基因,且ermB基因均同时存在于转座子Tn1545和Tn917;16株屎肠球供体菌和1株海氏肠球供体菌通过质粒接合转移试验后得到17株接合子,红霉素MIC≥512μg／ml,除原供体菌1株屎肠球菌阴性外,其余16株接合子全部携带ermB基因,并且有11株接合子ermB基因同时存在于Tn1545和Tn917,4株接合子ermB基因仅存在于Tn1545,1株接合子ermB基因仅存在于Tn917;30株肠球菌通过质粒接合转移试验后得到的30株金黄色葡萄球菌接合子,红霉素MIC≥512μg／ml,除原供体菌1株粪肠球菌和1株屎肠球菌阴性外,其余的28株接合子全部携带ermB基因,其中ermB基因同时存在于Tn1545和Tn917的为23株,4株接合子ermB基因仅存在于Tn1545,1株接合子ermB基因仅存在于Tn917。结论：肠球菌对红霉素的耐药性可以在同属同种、同属异种和异属之间进行传递;红霉素的耐药性与ermB基因存在一致,ermB基因与Tn1545和Tn917密切相关,ermB基因与Tn1545和Tn917可以在同属同种、同属异种和异属之间进行传递。

Transfer of erythromycin-resistance among strains and species of bacteria: plasmid conjugation method in enterococcal isolates

OBJECTIVE: To study if the resistance to macrolide in Enterococcus can be transferred between strains, and species of the same and different genera. METHODS: Agar dilution was used to screen 30 enterococcal isolates that were resistant to erythromycin. Conjugation was performed by filter mating method. The 30 donor bacteria included 13 strains of Enterococcus faecalis, 16 strains of E. faecium, and 1 strain of E. hirae. The recipient bacteria included 1 strain of E. faecalis sensitive to erythromycin and resistant to tetracycline, and 1 strain of Staphylococcus aureus with the MIC against erythromycin of 0.25 approximately 1 microg/ml. Polymerase chain reaction was used to test the existence of ermB gene and the tranposons Tn1545 and Tn917 in the enterococcal isolates before and after filter mating. RESULTS: The transfer rate between different strains and species of the same genus were all 100%. The MIC(50) and MIC(90) against erythromycin of 13 conjugates were both 512 microg/ml, and Tn1545 and Tn917 were found in the ermB gene of 12 conjugates. 17 conjugates were obtained from 16 strains of donor E. faecium and 1 strain of E. hirae with the MIC(50) and MIC(90) both of 512 microg/ml. The ermB gene was found in 16 of the 17 conjugates, and 11 of the 16 conjugates showed the existence of Tn1545 and Tn917, Tn1545 existed in the ermB gene of 4 conjugates, and Tn917 existed in the ermB gene of 1 conjugate. 30 conjugates of Staphylococcus aureus were obtained by plasmid conjugation and transfer with a transfer rate of 100% and the MIC(50) and MIC(90) both of 512 microg/ml. The ermB gene was found in 28 of the 30 conjugates. Both Tn1545 and Tn917 were found in the ermB gene of 23 of the 28 conjugates, Tn1545 was found in the ermB gene of 4 conjugates, and Tn917 was found in the ermB gene of 1 conjugate. CONCLUSION: The resistance to macrolide of Enterococcus, related with the existence of ermB gene and transposons Tn1545 and Tn917, can be transferred between strains and species of same and different genera.