Vancomycin Heteroresistance in vanM-type Enterococcus faecium.
Vancomycin Heteroresistance in vanM-type Enterococcus faecium.
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DOI：
10.1089/mdr.2019.0321
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发表时间：
2020-01
影响因子：
2.6
通讯作者：
Ying Zhou;Yang Yang-Yang;Li Ding;Chunhui Chen;Xiaogang Xu;Minggui Wang
中科院分区：
文献类型：
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作者：
Ying Zhou;Yang Yang-Yang;Li Ding;Chunhui Chen;Xiaogang Xu;Minggui Wang
尽管肠球菌存在万古霉素异质耐药性，但使用常规方法不易检测到，且其机制尚不清楚。在这项研究中，我们表征了临床 vanM 型屎肠球菌菌株万古霉素异质耐药性的分子机制。通过肉汤微量稀释和 Etest，原始屎肠球菌分离株 hVREm7 对万古霉素敏感。然而，在 Etest 抑制区内存在万古霉素抗性亚菌落。 hVREm7 进行了 3 次传代，以消除污染的可能性。选择hVREm7和三个抗性变异体来研究异质抗性机制。序列分析显示所有四种菌株均含有未改变的 vanM 簇。 Southern印迹分析表明，vanM在这三个变体中同时存在于染色体和染色体外，但在hVREm7中仅存在于染色体外。三个变体中携带vanM的染色体外DNA片段的大小均大于hVREm7中的，表明变体中vanM基因扩增的变化。一致地，变异株 VREm7-1 中 vanM 拷贝数和表达水平增加。这些结果表明，通过尚未确定的机制部分或完全扩增/转移 vanM 基因簇会导致 vanM 基因的拷贝数增加和表达增强，这有助于万古霉素异抗性屎肠球菌转化为高水平万古霉素抗性变体。
Although vancomycin heteroresistance exists in enterococci, it is not easily detected using routine methods and the mechanism is not clearly understood. In this study, we characterized the molecular mechanism underlying vancomycin heteroresistance in a clinical vanM-type Enterococcus faecium strain. The original E. faecium isolate, hVREm7, was susceptible to vancomycin by broth microdilution and Etest. However, vancomycin-resistant subcolonies were present within the Etest zone of inhibition. Three passages of hVREm7 were carried out to eliminate the possibility of contamination. hVREm7 and three resistant variants were selected to study the heteroresistance mechanism. Sequence analysis revealed that all four strains contained an unaltered vanM cluster. Southern blot analysis showed that vanM was present both chromosomally and extrachromosomally in the three variants, but only extrachromosomally in hVREm7. The size of the vanM-bearing extrachromosomal DNA fragments in the three variants was larger than that in hVREm7, indicating a variation of vanM gene amplification in the variants. Consistently, vanM copy number and expression level were increased in variant strain VREm7-1. These results suggest that partial or complete amplification/transfer of the vanM gene cluster by an as-yet-unidentified mechanism leads to increased copy number and augmented expression of the vanM gene, which contribute to the transformation of vancomycin-heteroresistant E. faecium into high-level vancomycin-resistant variants.