Mutation of RNA Polymerase β-Subunit Gene Promotes Heterogeneous-to-Homogeneous Conversion of β-Lactam Resistance in Methicillin-Resistant Staphylococcus aureus
Mutation of RNA Polymerase β-Subunit Gene Promotes Heterogeneous-to-Homogeneous Conversion of β-Lactam Resistance in Methicillin-Resistant Staphylococcus aureus
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DOI：
10.1128/aac.00720-13
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发表时间：
2013-10-01
影响因子：
4.9
通讯作者：
Hiramatsu, Keiichi
中科院分区：
文献类型：
--
作者：
Aiba, Yoshifumi;Katayama, Yuki;Hiramatsu, Keiichi
在耐甲氧西林金黄色葡萄球菌（MRSA）中已报道了三种类型的β-内酰胺耐药表型表达：异质性、同质性和耐药型。β-内酰胺耐药性的异质性到同质性转化被假定是由染色体突变（chr*）以及mecA基因的表达引起的。耐药型耐药是前MRSA菌株N315中发生的chr* 的独特表型，其mecA基因表达被完整的mecI基因强烈抑制。我们在这里报告，某些突变的rpoB基因，编码RNA聚合酶β亚基，属于chr*。我们研究了同质MRSA（homo-MRSA）菌株N315 Delta IP-H5（缩写为Delta IP-H5），其通过用8 mg/L亚胺培南选择从异质MRSA菌株N315 Delta IP获得。Delta IP-H5的全基因组测序揭示了rpoB基因中存在独特的突变rpoB（N967 I），导致RpoB的967位的Asn被Ile取代。通过构建回复突变体H5 rpoB（I967 N）菌株以及N315衍生突变体N315 rpoB（N967 I），证实了rpoB（N967 I）突变的效果。H5 rpoB（I967 N）恢复了异源耐药表型，N315 rpoB（N967 I）菌株显示出与典型的耐药型MRSA菌株N315 h4相似的耐药型表型。此外，随后的全基因组测序显示，N315 h4也有一个错义突变rpoB（R644 H）。引入rpoB（N967 I）突变伴随着自溶减少，倍增时间延长，并耐受甲氧西林的杀菌浓度。我们认为rpoB突变是MRSA菌株N315及其衍生菌株β-内酰胺耐药性从异源到同质表型转化的主要原因。
Three types of phenotypic expression of beta-lactam resistance have been reported in methicillin-resistant Staphylococcus aureus (MRSA): heterogeneous, homogeneous, and Eagle-type resistance. Heterogeneous-to-homogeneous conversion of beta-lactam resistance is postulated to be caused by a chromosomal mutation (chr*) in addition to the expression of the mecA gene. Eagle-type resistance is a unique phenotype of chr* occurring in pre-MRSA strain N315 whose mecA gene expression is strongly repressed by an intact mecI gene. We here report that certain mutations of the rpoB gene, encoding the RNA polymerase beta subunit, belong to chr*. We studied homogeneous MRSA (homo-MRSA) strain N315 Delta IP-H5 (abbreviated as Delta IP-H5), which was obtained from hetero-MRSA strain N315 Delta IP by selection with 8 mg/liter imipenem. Whole-genome sequencing of Delta IP-H5 revealed the presence of a unique mutation in the rpoB gene, rpoB(N967I), causing the amino acid replacement of Asn by Ile at position 967 of RpoB. The effect of the rpoB(N967I) mutation was confirmed by constructing a revertant H5 rpoB(I967N) strain as well as an N315-derived mutant, N315 rpoB(N967I). H5 rpoB(I967N) regained the hetero-resistance phenotype, and the N315 rpoB(N967I) strain showed an Eagle-type phenotype similar to that of the typical Eagle-type MRSA strain N315h4. Furthermore, subsequent whole-genome sequencing revealed that N315h4 also had a missense mutation of rpoB(R644H). Introduction of the rpoB(N967I) mutation was accompanied by decreased autolysis, prolonged doubling time, and tolerance to bactericidal concentrations of methicillin. We consider that rpoB mutations are the major cause for heterogeneous-to-homogeneous phenotypic conversion of beta-lactam resistance in MRSA strain N315 and its derived strains.