Shore Anna C, Lazaris Alexandros, Kinnevey Peter M, Brennan Orla M, Brennan Gráinne I, O'Connell Brian, Feßler Andrea T, Schwarz Stefan, Coleman David C
Microbiology Research Unit, Dublin Dental University Hospital, University of Dublin, Trinity College Dublin, Dublin, Ireland National MRSA Reference Laboratory, St. James's Hospital, Dublin, Ireland.
Microbiology Research Unit, Dublin Dental University Hospital, University of Dublin, Trinity College Dublin, Dublin, Ireland.
Antimicrob Agents Chemother. 2016 Apr 22;60(5):3007-15. doi: 10.1128/AAC.02949-15. Print 2016 May.
Linezolid is often the drug of last resort for serious methicillin-resistant Staphylococcus aureus (MRSA) infections. Linezolid resistance is mediated by mutations in 23S rRNA and genes for ribosomal proteins; cfr, encoding phenicol, lincosamide, oxazolidinone, pleuromutilin, and streptogramin A (PhLOPSA) resistance; its homologue cfr(B); or optrA, conferring oxazolidinone and phenicol resistance. Linezolid resistance is rare in S. aureus, and cfr is even rarer. This study investigated the clonality and linezolid resistance mechanisms of two MRSA isolates from patients in separate Irish hospitals. Isolates were subjected to cfr PCR, PhLOPSA susceptibility testing, 23S rRNA PCR and sequencing, DNA microarray profiling, spa typing, pulsed-field gel electrophoresis (PFGE), plasmid curing, and conjugative transfer. Whole-genome sequencing was used for single-nucleotide variant (SNV) analysis, multilocus sequence typing, L protein mutation identification, cfr plasmid sequence analysis, and optrA and cfr(B) detection. Isolates M12/0145 and M13/0401 exhibited linezolid MICs of 64 and 16 mg/liter, respectively, and harbored identical 23S rRNA and L22 mutations, but M12/0145 exhibited the mutation in 2/6 23S rRNA alleles, compared to 1/5 in M13/0401. Both isolates were sequence type 22 MRSA staphylococcal cassette chromosome mec type IV (ST22-MRSA-IV)/spa type t032 isolates, harbored cfr, exhibited the PhLOPSA phenotype, and lacked optrA and cfr(B). They differed by five PFGE bands and 603 SNVs. Isolate M12/0145 harbored cfr and fexA on a 41-kb conjugative pSCFS3-type plasmid, whereas M13/0401 harbored cfr and lsa(B) on a novel 27-kb plasmid. This is the first report of cfr in the pandemic ST22-MRSA-IV clone. Different cfr plasmids and mutations associated with linezolid resistance in genotypically distinct ST22-MRSA-IV isolates highlight that prudent management of linezolid use is essential.
利奈唑胺通常是治疗严重耐甲氧西林金黄色葡萄球菌（MRSA）感染的最后一线药物。利奈唑胺耐药性由23S rRNA和核糖体蛋白基因的突变介导；cfr基因编码对氯霉素、林可酰胺、恶唑烷酮、截短侧耳素和链阳菌素A（PhLOPSA）的耐药性；其同源基因cfr(B)；或optrA基因，赋予对恶唑烷酮和氯霉素的耐药性。利奈唑胺耐药性在金黄色葡萄球菌中罕见，而cfr基因更为罕见。本研究调查了来自爱尔兰两家不同医院患者的两株MRSA分离株的克隆性和利奈唑胺耐药机制。对分离株进行了cfr PCR、PhLOPSA药敏试验、23S rRNA PCR及测序、DNA微阵列分析、spa分型、脉冲场凝胶电泳（PFGE）、质粒消除和接合转移试验。全基因组测序用于单核苷酸变异（SNV）分析、多位点序列分型、L蛋白突变鉴定、cfr质粒序列分析以及optrA和cfr(B)检测。分离株M12/0145和M13/0401的利奈唑胺最低抑菌浓度（MIC）分别为64和16 mg/L，且具有相同的23S rRNA和L22突变，但M12/0145在6个23S rRNA等位基因中有2个发生突变，而M13/0401在5个中有1个发生突变。两株分离株均为序列型22的MRSA葡萄球菌盒式染色体mec IV型（ST22-MRSA-IV）/spa型t032分离株，携带cfr基因，表现出PhLOPSA表型，且缺乏optrA和cfr(B)。它们在PFGE条带和603个SNV上存在差异。分离株M12/0145在一个41 kb的接合型pSCFS3型质粒上携带cfr和fexA基因，而M13/0401在一个新的27 kb质粒上携带cfr和lsa(B)基因。这是大流行的ST22-MRSA-IV克隆中cfr基因的首次报道。在基因型不同的ST22-MRSA-IV分离株中，与利奈唑胺耐药性相关的不同cfr质粒和突变表明，谨慎管理利奈唑胺的使用至关重要。
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