Epidemiology and Infection

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Epidemiology and Infection (2010), 138:86-90 Cambridge University Press
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Short Report

Antimicrobial resistance

Quinolone-resistant Salmonella Typhi in South Africa, 2003–2007

A. M. SMITHa1a2 c1, N. GOVENDERa1 and K. H. KEDDYa1a2 the Group for Enteric, Respiratory and Meningeal Disease Surveillance in South Africa (GERMS-SA)

a1 Enteric Diseases Reference Unit, National Institute for Communicable Diseases, Johannesburg, South Africa
a2 University of the Witwatersrand, Johannesburg, South Africa
Article author query
smith am [PubMed]  [Google Scholar]
govender n [PubMed]  [Google Scholar]
keddy kh [PubMed]  [Google Scholar]


In South Africa, for the years 2003–2007, the Enteric Diseases Reference Unit received 510 human isolates of Salmonella Typhi, of which 27 were nalidixic acid-resistant [minimum inhibitory concentrations (MICs) 128–512 μg/ml] with reduced susceptibility to ciprofloxacin (MICs 0·125–0·5 μg/ml). Pulsed-field gel electrophoresis analysis of 19 available isolates differentiated them into five DNA pattern types; multiple-locus variable-number tandem repeat analysis differentiated the isolates into 10 types. This level of genetic diversity suggested that resistant strains usually emerged independently of one another. A 16- to 32-fold decrease in nalidixic acid MIC and a 2- to 8-fold decrease in ciprofloxacin MIC, was observed in the presence of an efflux pump inhibitor. All isolates were negative by PCR screening for qnr genes. Seven resistant isolates were further analysed for mutations in the quinolone resistance-determining region of gyrA, gyrB, parC and parE. No amino-acid mutations were identified in GyrB and ParE; all isolates showed amino-acid mutations in both GyrA and ParC. We conclude that amino-acid mutations in GyrA and ParC in combination with active efflux of antibiotic out of the bacterial cell are the probable mechanisms conferring quinolone resistance.

(Accepted June 04 2009)

(Online publication June 29 2009)

Key Words:Africa; quinolone resistance; Salmonella Typhi


c1 Author for correspondence: Dr A. M. Smith, Enteric Diseases Reference Unit, National Institute for Communicable Diseases, Private Bag X4, Sandringham, 2131, South Africa. (Email: anthonys@nicd.ac.za)