title: Whole genome analysis of linezolid resistance in Streptococcus pneumoniae reveals resistance and compensatory mutations.
abstract: BACKGROUND
  Several mutations were present in the genome of Streptococcus pneumoniae linezolid-resistant strains but the role of several of these mutations had not been experimentally tested. To analyze the role of these mutations, we reconstituted resistance by serial whole genome transformation of a novel resistant isolate into two strains with sensitive background. We sequenced the parent mutant and two independent transformants exhibiting similar minimum inhibitory concentration to linezolid.
  
  
  RESULTS
  Comparative genomic analyses revealed that transformants acquired G2576T transversions in every gene copy of 23S rRNA and that the number of altered copies correlated with the level of linezolid resistance and cross-resistance to florfenicol and chloramphenicol. One of the transformants also acquired a mutation present in the parent mutant leading to the overexpression of an ABC transporter (spr1021). The acquisition of these mutations conferred a fitness cost however, which was further enhanced by the acquisition of a mutation in a RNA methyltransferase implicated in resistance. Interestingly, the fitness of the transformants could be restored in part by the acquisition of altered copies of the L3 and L16 ribosomal proteins and by mutations leading to the overexpression of the spr1887 ABC transporter that were present in the original linezolid-resistant mutant.
  
  
  CONCLUSIONS
  Our results demonstrate the usefulness of whole genome approaches at detecting major determinants of resistance as well as compensatory mutations that alleviate the fitness cost associated with resistance.
authors: Centre de recherche en Infectiologie du Centre de recherche du CHUL, Infectiologie et Immunologie, Faculté de Médecine, Université Laval, Québec, Canada.
authors: Dewan S
authors: DS
authors: Billal
authors: Jie
authors: J
authors: Feng
authors: Philippe
authors: P
authors: Leprohon
authors: Danielle
authors: D
authors: Légaré
authors: Marc
authors: M
authors: Ouellette
mesh_terms: D000081:Acetamides / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D016680:Genome, Bacterial; D000069349:Linezolid; D008826:Microbial Sensitivity Tests; D009154:Mutation; D023303:Oxazolidinones / Q000494:pharmacology*; D012338:RNA, Ribosomal, 23S / Q000235:genetics; D017422:Sequence Analysis, DNA; D013296:Streptococcus pneumoniae / Q000187:drug effects / Q000235:genetics*; D014169:Transformation, Bacterial
chemical_list: D000081:Acetamides; D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D023303:Oxazolidinones; D012338:RNA, Ribosomal, 23S; D000069349:Linezolid