Phenotypes and genotypes of erythromycin-resistant Streptococcus pyogenes strains in Italy and heterogeneity of inducibly resistant strains
Phenotypes and genotypes of erythromycin-resistant Streptococcus pyogenes strains in Italy and heterogeneity of inducibly resistant strains
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DOI：
10.1128/aac.43.8.1935
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发表时间：
1999-08-01
影响因子：
4.9
通讯作者：
Varaldo, PE
中科院分区：
文献类型：
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作者：
Giovanetti, E;Montanari, MP;Varaldo, PE
共检测了387株红霉素耐药（MIC，大于或等于1 μ g/ml）化脓性链球菌的临床菌株，所有菌株均于1995年至1998年在意大利实验室分离。通过红霉素-克林霉素双纸片法，203株（52.5%）被分配到最近描述的M表型，120株（31.0%）被分配到诱导型大环内酯类、林可酰胺和链阳性菌素B耐药（iMLS）表型，64株（16.5%）被分配到组成型MLS耐药（cMLS）表型。通过比较在正常试验条件下测定的克林霉素MIC和在0.05 μ g红霉素/ml预生长诱导后测定的克林霉素MIC，证实了iMLS菌株耐药性的诱导特征。然后测定并比较红霉素、克拉霉素、阿奇霉素、交沙霉素、螺旋霉素和酮内酯HMR 3004的MIC。观察到cMLS表型分离株（除一种菌株外，所有菌株的HMR 3004 MIC均为0.5 - 8 μ g/ml，其他药物的MIC均>128 μ g/ml）和M表型分离株（仅记录了对14-和15-元大环内酯类的耐药性，MIC为2 - 32 μ g/ml）的敏感性模式均相同。相反，在iMLS表型的分离株中观察到异质性敏感性模式，其被细分为三种不同的亚型，称为iMLS-A、iMLS-B和iMLS-C。iMLS-A菌株（n = 84）对14-、15-和16-元大环内酯类具有高度耐药性，并表现出对HMR 3004低水平耐药性的敏感性降低。iMLS-B菌株（n = 12）对14元和15元大环内酯类高度耐药，对16元大环内酯类敏感（但诱导后对交沙霉素高度耐药），对HMR 3004敏感（但诱导后中度或耐药）。iMLS-C菌株（n = 24）对14元和15元大环内酯类药物的耐药性水平较低（诱导后红霉素MIC增加2 - 4倍），对16元大环内酯类药物敏感（但诱导后对交沙霉素耐药），并且在诱导后仍对HMR 3004敏感。用PCR方法对100株不同群的分离株进行红霉素耐药基因的检测。检测的所有cMLS和iMLS-A分离株均具有ermAM（ermB）基因，而所有iMLS-B和iMLS-C分离株均具有ermTR基因（在其他组的分离株中均未发现甲基化酶基因）。M分离株仅具有大环内酯外排（mefA）基因，该基因也见于cMLS、iMLS-A、iMLS-B和iMLS-C分离株的不同比例中。三种iMLS亚型很容易区分的三个磁盘测试通过添加交沙霉素磁盘的红霉素和克林霉素磁盘的传统双磁盘测试。四环素耐药性在任何iMLS-A亚型分离株中均未检测到，而在超过90%的iMLS-B和iMLS-C分离株中均观察到。
A total of 387 clinical strains of erythromycin-resistant (MIC, greater than or equal to 1 mu g/ml) Streptococcus pyogenes, all isolated in Italian laboratories from 1995 to 1998, were examined. By the erythromycin-clindamycin double-disk test, 203 (52.5%) strains were assigned to the recently described M phenotype, 120 (31.0%) were assigned to the inducible macrolide, lincosamide, and streptogramin B resistance (iMLS) phenotype, and 64 (16.5%) were assigned to the constitutive MLS resistance (cMLS) phenotype. The inducible character of the resistance of the iMLS strains was confirmed by comparing the clindamycin MICs determined under normal testing conditions and those determined after induction by pregrowth in 0.05 mu g of erythromycin per mi. The MICs of erythromycin, clarithromycin, azithromycin, josamycin, spiramycin, and the ketolide HMR3004 were then determined and compared. Homogeneous susceptibility patterns were observed for the isolates of the cMLS phenotype (for all but one of the strains, HMR3004 MICs were 0.5 to 8 mu g/ml and the MICs of the other drugs were >128 mu g/ml) and those of the M phenotype (resistance only to the 14- and 15-membered macrolides was recorded, with MICs of 2 to 32 mu g/ml). Conversely, heterogeneous susceptibility patterns were observed in the isolates of the iMLS phenotype, which were subdivided into three distinct subtypes designated iMLS-A, iMLS-B, and iMLS-C. The iMLS-A strains (n = 84) were highly resistant to the 14-, 15-, and 16-membered macrolides and demonstrated reduced susceptibility to low-level resistance to HMR3004. The iMLS-B strains (n = 12) were highly resistant to the 14- and 15-membered macrolides, susceptible to the 16-membered macrolides (but highly resistant to josamycin after induction), and susceptible to HMR3004 (but intermediate or resistant after induction). The iMLS-C strains (n = 24) had lower levels of resistance to the 14- and 15-membered macrolides (with erythromycin MICs increasing two to four times after induction), were susceptible to the 16-membered macrolides (but resistant to josamycin after induction), and remained susceptible to HMR3004, also after induction. The erythromycin resistance genes in 100 isolates of the different groups were investigated by PCR. All cMLS and iMLS-A isolates tested had the ermAM (ermB) gene, whereas all iMLS-B and iMLS-C isolates had the ermTR gene (neither methylase gene was found in isolates of other groups). The M isolates had only the macrolide efflux (mefA) gene, which was also found in variable proportions of cMLS, iMLS-A, iMLS-B, and iMLS-C isolates. The three iMLS subtypes were easily differentiated by a triple-disk test set up by adding a josamycin disk to the erythromycin and clindamycin disks of the conventional double-disk test. Tetracycline resistance was not detected in any isolate of the iMLS-A subtype, whereas it was observed in over 90% of both iMLS-B and iMLS-C isolates.