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Journal of Clinical Microbiology, June 1998, p. 1595-1600, Vol. 36, No. 6
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Molecular Analysis of and Identification of Antibiotic Resistance Genes in Clinical Isolates of Salmonella typhi from India

Philippa M. A. Shanahan,1 Mary V. Jesudason,2 Christopher J. Thomson,1 and Sebastian G. B. Amyes1,*

Department of Medical Microbiology, University of Edinburgh, Edinburgh EH8 9AG, United Kingdom,1 and Department of Clinical Microbiology, Christian Medical College and Hospital, Vellore-632 004, India2

Received 28 July 1997/Returned for modification 1 November 1997/Accepted 15 March 1998

A representative sample of 21 Salmonella typhi strains isolated from cultures of blood from patients at the Christian Medical College and Hospital, Vellore, India, were tested for their susceptibilities to various antimicrobial agents. Eleven of the S. typhi strains possessed resistance to chloramphenicol (256 mg/liter), trimethoprim (64 mg/liter), and amoxicillin (>128 mg/liter), while four of the isolates were resistant to each of these agents except for amoxicillin. Six of the isolates were completely sensitive to all of the antimicrobial agents tested. All the S. typhi isolates were susceptible to cephalosporin agents, gentamicin, amoxicillin plus clavulanic acid, and imipenem. The antibiotic resistance determinants in each S. typhi isolate were encoded by one of four plasmid types. Plasmid-mediated antibiotic resistance genes were identified with specific probes in hybridization experiments; the genes responsible for chloramphenicol, trimethoprim, and ampicillin resistance were chloramphenicol acetyltransferase type I, dihydrofolate reductase type VII, and TEM-1 beta -lactamase, respectively. Pulsed-field gel electrophoresis analysis of XbaI-generated genomic restriction fragments identified a single distinct profile (18 DNA fragments) for all of the resistant isolates. In comparison, six profiles, different from each other and from the resistance profile, were recognized among the sensitive isolates. It appears that a single strain containing a plasmid conferring multidrug-resistance has emerged within the S. typhi bacterial population in Vellore and has been able to adapt to and survive the challenge of antibiotics as they are introduced into clinical medicine.

* Corresponding author. Mailing address: Department of Medical Microbiology, University of Edinburgh, Teviot Place, Edinburgh EH8 9AG, United Kingdom. Phone: 44 131 650 3163. Fax: 44 131 650 6882. E-mail: s.g.b.amyes{at}ed.ac.uk.

Journal of Clinical Microbiology, June 1998, p. 1595-1600, Vol. 36, No. 6
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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