title: Characterization of non-classical quinolone resistance inSalmonella entericaserovar Typhi: Report of a novel mutation ingyrB gene and diagnostic challenges.
abstract: OBJECTIVE
  To establish the relative importance ofSalmonella entericaserovar Typhi with non-classical quinolone resistance.
  
  
  METHODS
  Eight hundred and ninety-one isolates ofS.Typhi, isolated between 2004 and 2011, were tested for antibiotic susceptibility determination using disc diffusion and E-test. The mechanisms of fluoroquinolone resistance were studied in a sub-set of the NALS(nalidixic acid susceptible) isolates by wave nucleic acid fragment analysis of PCR products fromgyrA,gyrB,parCandparEand from the plasmid borne determinants:qnrA,B,S; aac(6')-Ib-cr andqepA. To assess genetic relatedness multi-locus variable number tandem repeat analysis was carried out using five loci.
  
  
  RESULTS
  Eighty isolates with a nalidixic acid MIC of <32 mg/L (NALS) and a ciprofloxacin MIC of >0.064 mg/L CIPI(ciprofloxacin reduced susceptibility) were found. In 36 NALSCIPIisolates two distinct genotypes were identified when compared with 16 susceptible controls: Group B (n= 34), mutation ingyrBat codon 464, NAL MIC of 3-12 mg/L and CIP MIC of 0.064-0.5 mg/L.; and Group C, mutation ingyrAat codon 83 (n= 2) NAL MIC of 16 mg/L and CIP MIC of 0.25-0.38 mg/L. Group B isolates were found in different strain backgrounds as defined by MLVA.
  
  
  CONCLUSIONS
  The use of nalidixic acid to screen for reduced susceptibility to fluoroquinolones inS.Typhi misses CIPI-NALSisolates, an established phenotype in India.
authors.affiliation: Department of Biosciences, Jamia Millia Islamia, New Delhi 110025, India; Department of Microbiology, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi 110029, India.
authors.forename: Ruchi
authors.initials: R
authors.lastname: Gupta
authors.affiliation: Department of Microbiology, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi 110029, India.
authors.forename: Rajni
authors.initials: R
authors.lastname: Gaind
authors.affiliation: Norwich Medical School, University of East Anglia, NRP Innovation Centre, Norwich Research Park, Colney Lane, Norwich, Norfolk NR4 7GJ, United Kingdom.
authors.forename: John
authors.initials: J
authors.lastname: Wain
authors.affiliation: Department of Microbiology, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi 110029, India.
authors.forename: Monorama
authors.initials: M
authors.lastname: Deb
authors.affiliation: National Institute of Pathology, Indian Council of Medical Research, New Delhi 110029, India.
authors.forename: Laishram Chandreshwor
authors.initials: LC
authors.lastname: Singh
authors.affiliation: Department of Biosciences, Jamia Millia Islamia, New Delhi 110025, India.
authors.forename: Seemi Farhat
authors.initials: SF
authors.lastname: Basir
keywords: DHPLC; Decreased ciprofloxacin susceptibility; Salmonella Typhi; VNTR; gyrB mutation