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Molecular Analysis of High-Level Ciprofloxacin Resistance in Salmonella enterica Serovar Typhi and S. Paratyphi A: Need to Expand the QRDR Region?

M. R. Capoor, D. Nair, N. S. Walia, R. S. Routela, S. S. Grover, M. Deb, P. Aggarwal, P. K. Pillai and P. J. Bifani
Epidemiology and Infection
Vol. 137, No. 6 (Jun., 2009), pp. 871-878
Stable URL: http://www.jstor.org/stable/30221688
Page Count: 8
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Molecular Analysis of High-Level Ciprofloxacin Resistance in Salmonella enterica Serovar Typhi and S. Paratyphi A: Need to Expand the QRDR Region?
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Abstract

Fourteen strains of S. Typhi (n = 13) and S. Paratyphi A (n= 1) resistant to ciprofloxacin were compared with 30 ciprofloxacin decreased-susceptibility strains on the basis of qnr plasmid analysis, and nucleotide substitutions at gyrA, gyrB, parC and parE. In ciprofloxacin-resistant strains, five S. Typhi and a single S. Paratyphi A showed triple mutations in gyrA ( $Ser^{83}\rightarrowPhe, Asp^{87}\rightarrowAsn, Glu^{113}\rightarrowGly$ ) and a novel mutation outside the quinolone resistance determining region (QRDR) ( $Met^{52}\rightarrowLeu$ ). Novel mutations were also discovered in an isolate (minimum inhibitory concentration 8 µg/ml) in gyrA gene $Asp^{76}\rightarrowAsn$ and outside the QRDR $Leu^{44}\rightarrowIle$ . Out of 30 isolates with reduced susceptibility, single mutation was found in 12 strains only. Genes encoding qnr plasmid (qnr A, qnr B, AAC1-F) were not detected in ciprofloxacin-resistant or decreased-susceptibility strains. Antimicrobial surveillance coupled with molecular analysis of fluoroquinolone resistance is warranted for reconfirming novel and established molecular patterns of resistance, which is quintessential for reappraisal of enteric fever therapeutics.

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