B族链球菌的红霉素耐药基因研究

目的 比较不同地区B族链球菌（GBS）对红霉素耐药性的差异及耐药基因谱特点。方法 用琼脂稀释法，测定红霉素、克林霉素对不同地区（北京，广州，俄罗斯圣彼得堡）的113株GBS的最低抑菌浓度（MIC），同时用PCR和核酸杂交的方法，检测红霉素耐药基因mreA、mefA、ermA、ermB、ermC在该批菌株中的出现规律及其与红霉素耐药性的关系。结果 （1）北京、广州两地GBS菌株总耐药率为46％，与克林霉素耐药性的一致率为93．8％；所有ermA基因均来自北京菌株，而广州菌株不含该基因。（2）含ermA和（或）ermB基因的GBS占所有菌株的30．09％，其耐药率高达97．06％，在已检测的GBS菌株中未发现ermC基因。（3）分别有53株和18株含mreA和mefA的GBS以及1株含ermA的菌株仍对红霉素敏感。2株GBS不含上述任何一种基因，但仍对红霉素耐药。结论 （1）北京、广州两地GBS对红霉素普遍具有较高的耐药率，且与大环内酯－林可霉素－链阳性霉素B类抗生素之间存在较严重的交叉耐药，临床使用抗生素时应尽量避免重复选择此类抗生素；（2）ermA和ermB是决定我国北京、广州GBS对红霉素耐药的重要基因；（3）GBS的耐药性还有其他分子生物学机制参与。

Erythromycin resistant genes in group B streptococcus

Objective Group B streptococcus (GBS) is a bacterium commonly found in the genital tracts of women and the leading pathogen of the infection during the perinatal stage. It was proved that the neonatal GBS infection was related to the mother carrying GBS during pregnancy or delivery. Several countries have had consensus guidelines to give intrapartum prophylactic antibiotics to the parturients in order to reduce both the maternal and the neonatal incidences of GBS infection. Among those antibiotics, erythromycin is one of the most commonly used; however, in recent years, it has been a severe problem for the GBS being more resistant to the macrolides, especially erythromycin. There are limited studies concerning erythromycin susceptibility profiles of GBS in China. This study was carried out to compare the different susceptibility profiles to erythromycin and clindamycin of GBS strains isolated in 3 different cities, and the different patterns of erythromycin resistant genes in these strains, in order to provide a genetic basis for reasonable use of erythromycin. Methods Erythromycin and clindamycin susceptibility test of the GBS strains isolated in Beijing, Guangzhou and St. Petersburg was performed by using standard agar dilution method by the National Committee for Clinical Laboratory Standards. The presence of mreA, mefA, ermA, ermB, ermC genes were determined by PCR amplification and Southern blot hybridization. Results Forty six percent of the isolates from Beijing and Guangzhou were erythromycin resistant, and the susceptibility profiles were 93.8% identical with those of clindamycin. The ermA gene was found only in the isolates of Beijing, while no ermA gene was detected in Guangzhou strains. ermA and/or ermB were determined in 30.09% of the strains, 97.06% of which were erythromycin resistant, while no ermC gene was found. There were 53 and 18 strains with the presence of mreA and/or mefA gene(s) respectively, and 1 ermA positive strain that were still sensitive to erythromycin, while 2 strains showed resistance without any of the 5 genes detected. Conclusions There was a high erythromycin resistance rate among the GBS strains isolated in Beijing and Guangzhou, and the cross resistance to Macrolide Lincosamide Streptogramin B (MLS B) antibiotics was severe,which indicated that repeated use of MLS B antibiotics should be avoided in clinical work. The ermA and ermB were important erythromycin resistance determinants of the GBS in China. Many sensitive strains with positive erythromycin resistance gene(s) could be potentially reversed to resistant strains. There should be some other mechanisms responsible for the erythromycin resistance of GBS.