title: Infrequent occurrence of single mutations in topoisomerase IV and DNA gyrase genes among US levofloxacin-susceptible clinical isolates of Streptococcus pneumoniae from nine institutions (1999-2003).
abstract: OBJECTIVE
  Prevalence of single quinolone-resistance determining region (QRDR) mutations in Streptococcus pneumoniae was studied from nine institutions over 5 years to track the incidence of single QRDR mutations.
  
  
  METHODS
  All 1106 levofloxacin-susceptible pneumococci (MICs < or = 2.0 mg/L) identified from 1112 total isolates (99.5% susceptibility) in TRUST 3 (1999), TRUST 5 (2001) and TRUST 7 (2003) surveillance studies from the same nine hospitals in nine states were screened for QRDR mutations. Using pyrosequencing, the strains were screened for mutations corresponding to hot spots Asp-78, Ser-79 and Asp-83 in ParC; Asp-80, Ser-81 and Glu-85 in GyrA; Asp-435 in ParE and Asp-435 in GyrB. DNA sequencing of QRDRs was performed to confirm mutations.
  
  
  RESULTS
  No QRDR mutations were found in any of the isolates with levofloxacin MICs < or = 0.5 mg/L and no gyrA or gyrB QRDR mutations were found in any of the screened isolates (MICs < or = 2 mg/L). Four single-step QRDR mutants with the following amino acid substitutions were found: ParE Asp-435 to Asn (isolated in 1999 in Colorado); ParC Asp-83 to Asn (isolated in 2001 in Kentucky); ParC Ser-79 to Phe (isolated in 2003 in Indiana) and ParC Ser-79 to Tyr (isolated in 2003 in California). These non-clonal strains had levofloxacin MICs of 1 mg/L and were non-susceptible to ciprofloxacin (MIC 2-4 mg/L).
  
  
  CONCLUSIONS
  Overall prevalence of single QRDR mutations in levofloxacin-susceptible S. pneumoniae with MICs of < or = 2 mg/L was 0.4% (4/1106) and has remained <1% within nine institutions over 5 years (1999-2003).
authors.affiliation: Johnson & Johnson Pharmaceutical Research & Development L.L.C., 1000 Route 202, Raritan, NJ, USA. tdavies@prdus.jnj.com
authors.forename: Todd A
authors.initials: TA
authors.lastname: Davies
authors.forename: Y Cheung
authors.initials: YC
authors.lastname: Yee
authors.forename: Raul
authors.initials: R
authors.lastname: Goldschmidt
authors.forename: Karen
authors.initials: K
authors.lastname: Bush
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Sahm
authors.forename: Alan
authors.initials: A
authors.lastname: Evangelista
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D027081:DNA Gyrase / Q000235:genetics*; D027101:DNA Topoisomerase IV / Q000235:genetics*; D024881:Drug Resistance, Bacterial / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D064704:Levofloxacin; D008826:Microbial Sensitivity Tests; D009154:Mutation / Q000235:genetics*; D015242:Ofloxacin / Q000494:pharmacology*; D011008:Pneumococcal Infections / Q000453:epidemiology / Q000382:microbiology; D013296:Streptococcus pneumoniae / Q000201:enzymology* / Q000235:genetics*; D014481:United States / Q000453:epidemiology
chemical_list: D000900:Anti-Bacterial Agents; D064704:Levofloxacin; D015242:Ofloxacin; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase