Identification of a novel tedizolid resistance mutation in rpoB of MRSA after in vitro serial passage.

Identification of a novel tedizolid resistance mutation in rpoB of MRSA after in vitro serial passage.

OBJECTIVES Tedizolid is an oxazolidinone antimicrobial with activity against Gram-positive bacteria, including MRSA. Tedizolid resistance is uncommon and tedizolid's capacity to select for cross-resistance to other antimicrobials is incompletely understood. The objective of this study was to further explore the phenotypic and genetic basis of tedizolid resistance in MRSA. METHODS We selected for tedizolid resistance in an MRSA laboratory strain, N315, by serial passage until an isolate with an MIC ≥1 log2 dilution above the breakpoint for resistance (≥2 mg/L) was recovered. This isolate was subjected to WGS and susceptibility to a panel of related and unrelated antimicrobials was tested in order to determine cross-resistance. Homology modelling was performed to evaluate the potential impact of the mutation on target protein function. RESULTS After 10 days of serial passage we recovered a phenotypically stable mutant with a tedizolid MIC of 4 mg/L. WGS revealed only one single nucleotide variant (A1345G) in rpoB, corresponding to amino acid substitution D449N. MICs of linezolid, chloramphenicol, retapamulin and quinupristin/dalfopristin increased by ≥2 log2 dilutions, suggesting the emergence of the so-called 'PhLOPSa' resistance phenotype. Susceptibility to other drugs, including rifampicin, was largely unchanged. Homology models revealed that the mutated residue of RNA polymerase would be unlikely to directly affect oxazolidinone action. CONCLUSIONS To the best of our knowledge, this is the first time that an rpoB mutation has been implicated in resistance to PhLOPSa antimicrobials. The mechanism of resistance remains unclear, but is likely indirect, involving σ-factor binding or other alterations in transcriptional regulation.

目的 泰地唑胺是一种恶唑烷酮类抗菌药物，对革兰阳性菌包括耐甲氧西林金黄色葡萄球菌（MRSA）具有抗菌活性。泰地唑胺耐药并不常见，且其对其他抗菌药物产生交叉耐药的能力尚未完全明确。本研究的目的是进一步探究MRSA对泰地唑胺耐药的表型和遗传基础。 方法 我们通过连续传代在一株MRSA实验室菌株N315中筛选泰地唑胺耐药株，直至获得一株最低抑菌浓度（MIC）比耐药折点（≥2mg/L）高≥1个log₂稀释度的分离株。对该分离株进行全基因组测序（WGS），并检测其对一组相关和不相关抗菌药物的敏感性以确定交叉耐药情况。进行同源建模以评估突变对靶蛋白功能的潜在影响。 结果 经过10天的连续传代，我们获得了一株表型稳定的突变株，其泰地唑胺MIC为4mg/L。全基因组测序显示rpoB基因仅有一个单核苷酸变异（A1345G），对应氨基酸替换为D449N。利奈唑胺、氯霉素、瑞他帕林和奎奴普丁/达福普汀的MIC升高≥2个log₂稀释度，提示出现了所谓的“PhLOPSa”耐药表型。对其他药物包括利福平的敏感性基本未改变。同源模型显示RNA聚合酶的突变残基不太可能直接影响恶唑烷酮的作用。 结论 据我们所知，这是首次发现rpoB突变与对PhLOPSa类抗菌药物的耐药相关。耐药机制仍不清楚，但可能是间接的，涉及σ因子结合或转录调控的其他改变。