title: Multiple pathways of cross-resistance to glycopeptides and daptomycin in persistent MRSA bacteraemia.
abstract: BACKGROUND
  The development of non-susceptibility to glycopeptides and daptomycin in MRSA during persistent bacteraemia has become a significant therapeutic challenge. However, the in vivo evolution and mechanism of the dual resistance have remained incompletely understood.
  
  
  METHODS
  A series of MRSA blood isolates with incremental non-susceptibility to glycopeptides and daptomycin were consecutively recovered from a bacteraemic patient who was failing chemotherapy. The evolutionary pathways during conversion from a glycopeptide- and daptomycin-susceptible phenotype into a vancomycin-intermediate Staphylococcus aureus (VISA) and a daptomycin-resistant S. aureus (DRSA) phenotype were then traced by WGS of the isogenic strains.
  
  
  RESULTS
  A total of six non-synonymous mutations and three evolutionary pathways were identified during the development of the VISA/DRSA phenotype. The first pathway involved two steps of evolution, with an initial 1 bp insertion into yycH and a subsequent gain-in-function point mutation in mprF (S295L). The two mutations were correlated with heteroresistance to daptomycin/vancomycin and full development of the VISA/DRSA phenotype. The second pathway involved an 11 bp deletion mutation in yycH and point mutations at two genes, correlating with the development of the VISA phenotype and heteroresistance to daptomycin. Mutation in mprF (S295L) and a 5 bp deletion mutation in yycH were identified in the third pathway and corresponded to conversion into the full VISA/DRSA phenotype. The mutations in yycH resulted in premature terminations of YycH with variable lengths.
  
  
  CONCLUSIONS
  Multiple evolutionary pathways involving yycH and mprF can proceed simultaneously and may mediate cross-resistance to glycopeptides and daptomycin during persistent MRSA bacteraemia under antibiotic selective pressure.
authors.affiliation: Division of Paediatric Infectious Diseases, Department of Paediatrics, Chang Gung Children's Hospital and Chang Gung Memorial Hospital, 333 Taoyuan, Taiwan College of Medicine, Chang Gung University, 333 Taoyuan, Taiwan james.ped@gmail.com.
authors.forename: Chih-Jung
authors.initials: CJ
authors.lastname: Chen
authors.affiliation: Division of Paediatric Infectious Diseases, Department of Paediatrics, Chang Gung Children's Hospital and Chang Gung Memorial Hospital, 333 Taoyuan, Taiwan College of Medicine, Chang Gung University, 333 Taoyuan, Taiwan.
authors.forename: Yhu-Chering
authors.initials: YC
authors.lastname: Huang
authors.affiliation: Division of Paediatric Infectious Diseases, Department of Paediatrics, Chang Gung Children's Hospital and Chang Gung Memorial Hospital, 333 Taoyuan, Taiwan College of Medicine, Chang Gung University, 333 Taoyuan, Taiwan.
authors.forename: Cheng-Hsu
authors.initials: CH
authors.lastname: Chiu
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D016470:Bacteremia / Q000188:drug therapy / Q000382:microbiology*; D004252:DNA Mutational Analysis; D017576:Daptomycin / Q000494:pharmacology* / Q000627:therapeutic use; D024881:Drug Resistance, Bacterial; D019143:Evolution, Molecular; D016680:Genome, Bacterial; D006020:Glycopeptides / Q000494:pharmacology* / Q000627:therapeutic use; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D009154:Mutation; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA; D013203:Staphylococcal Infections / Q000188:drug therapy / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents; D006020:Glycopeptides; D017576:Daptomycin