title: First Report of cfr-Carrying Plasmids in the Pandemic Sequence Type 22 Methicillin-Resistant Staphylococcus aureus Staphylococcal Cassette Chromosome mec Type IV Clone.
abstract: 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.
authors.affiliation: 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.
authors.forename: Anna C
authors.initials: AC
authors.lastname: Shore
authors.affiliation: Microbiology Research Unit, Dublin Dental University Hospital, University of Dublin, Trinity College Dublin, Dublin, Ireland.
authors.forename: Alexandros
authors.initials: A
authors.lastname: Lazaris
authors.affiliation: Microbiology Research Unit, Dublin Dental University Hospital, University of Dublin, Trinity College Dublin, Dublin, Ireland.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Kinnevey
authors.affiliation: Microbiology Research Unit, Dublin Dental University Hospital, University of Dublin, Trinity College Dublin, Dublin, Ireland.
authors.forename: Orla M
authors.initials: OM
authors.lastname: Brennan
authors.affiliation: 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.
authors.forename: Gráinne I
authors.initials: GI
authors.lastname: Brennan
authors.affiliation: National MRSA Reference Laboratory, St. James's Hospital, Dublin, Ireland Department of Clinical Microbiology, School of Medicine, Trinity College Dublin, St. James's Hospital, Dublin, Ireland.
authors.forename: Brian
authors.initials: B
authors.lastname: O'Connell
authors.affiliation: Institute of Farm Animal Genetics, Friedrich Loeffler Institut, Neustadt-Mariensee, Germany.
authors.forename: Andrea T
authors.initials: AT
authors.lastname: Feßler
authors.affiliation: Institute of Farm Animal Genetics, Friedrich Loeffler Institut, Neustadt-Mariensee, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Schwarz
authors.affiliation: Microbiology Research Unit, Dublin Dental University Hospital, University of Dublin, Trinity College Dublin, Dublin, Ireland david.coleman@dental.tcd.ie.
authors.forename: David C
authors.identifier: 0000-0003-1797-2888
authors.initials: DC
authors.lastname: Coleman
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002876:Chromosomes, Bacterial / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000235:genetics*; D010957:Plasmids / Q000235:genetics; D012338:RNA, Ribosomal, 23S / Q000235:genetics; D013203:Staphylococcal Infections / Q000235:genetics; D013211:Staphylococcus aureus / Q000187:drug effects / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D012338:RNA, Ribosomal, 23S