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JAC Advance Access published online on October 28, 2006
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkl391
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© The Author 2006. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org
Received April 7, 2006
Revised August 20, 2006
Accepted September 6, 2006

Original article

Molecular characterization of ciprofloxacin-resistant Salmonella enterica serovar Typhi and Paratyphi A causing enteric fever in India

R. Gaind 1, B. Paglietti 2, M. Murgia 2, R. Dawar 1, S. Uzzau 2, P. Cappuccinelli 2, M. Deb 1, P. Aggarwal 1, and S. Rubino 2 *

1 Department of Microbiology, Safdarjung Hospital and Assoc VMMC, New Delhi, India
2 Department of Biomedical Sciences, Division of Experimental and Clinical Microbiology, University of Sassari, Sassari, Italy

* To whom correspondence should be addressed.
S. Rubino, E-mail: rubino{at}uniss.it


  Abstract

Objectives: To define the genetic characteristics and resistance mechanisms of clinical isolates of Salmonella enterica serovar Typhi (S. Typhi) and S. enterica serovar Paratyphi A (S. Paratyphi A) exhibiting high-level fluoroquinolones resistance.

Methods: Three S. Typhi and two S. Paratyphi A ciprofloxacin-resistant isolates (MICs > 4 mg/L) were compared with isolates with reduced susceptibility to ciprofloxacin (MICs 0.125-1 mg/L) by PFGE, plasmid analysis, presence of integrons and nucleotide changes in topoisomerase genes.

Results: In S. Typhi and Paratyphi A, a single gyrA mutation (Ser-83->Phe or Ser-83->Tyr) was associated with reduced susceptibility to ciprofloxacin (MICs 0.125-1 mg/L); an additional mutation in parC (Ser-80->Ile, Ser-80->Arg, Asp-69->Glu or Gly-78->Asp) was accompanied by an increase in ciprofloxacin MIC (≥ 0.5 mg/L). Three mutations conferred ciprofloxacin resistance: two in gyrA (Ser-83->Phe and Asp-87->Asn or Asp-87->Gly) and one in parC. This is the first report of parC mutations in S. Typhi. Ciprofloxacin-resistant S. Typhi and S. Paratyphi A differed in their MICs and mutations in gyrA and parC. Moreover S. Typhi harboured a 50 kb transferable plasmid carrying a class 1 integron (dfrA15/aadA1) that confers resistance to co-trimoxazole and tetracycline but not to ciprofloxacin. PFGE revealed undistinguishable XbaI fragment patterns in ciprofloxacin-resistant S. Typhi as well as in S. Paratyphi A isolates and showed that ciprofloxacin-resistant S. Typhi have emerged from a clonally related isolate with reduced susceptibility to ciprofloxacin after sequential acquisition of a second mutation in gyrA.

Conclusions: To our knowledge this is the first report of molecular characterization of S. Typhi with full resistance to ciprofloxacin. Notably, the presence of a plasmid-borne integron in ciprofloxacin-resistant S. Typhi may lead to a situation of untreatable enteric fever.

Keywords: Salmonella enterica serovar Paratyphi A; DNA gyrase; topoisomerase IV; integrons; high-level fluoroquinolone resistance.
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