Epidemiology and Infection

Original Papers


Molecular analysis of high-level ciprofloxacin resistance in Salmonella enterica serovar Typhi and S. Paratyphi A: need to expand the QRDR region?

M. R. CAPOORa1, D. NAIRa1 c1, N. S. WALIAa1, R. S. ROUTELAa2, S. S. GROVERa2, M. DEBa1, P. AGGARWALa1, P. K. PILLAIa3 and P. J. BIFANIa4

a1 Department of Microbiology, Vardhman Mahaveer Medical College and Safdarjung Hospital, New Delhi, India

a2 Department of Biotechnology, National Institute of Communicable Diseases, New Delhi, India

a3 Department of Microbiology, Majeedia Hospital, New Delhi, India

a4 Department of Molecular Biology, Pasteur Institute, Brussels, Belgium


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 (Ser83→Phe, Asp87→Asn, Glu133→Gly) and a novel mutation outside the quinolone resistance determining region (QRDR) (Met52→Leu). Novel mutations were also discovered in an isolate (minimum inhibitory concentration 8 μg/ml) in gyrA gene Asp76→Asn and outside the QRDR Leu44→Ile. 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.

(Accepted June 18 2008)

(Online publication August 08 2008)


c1 Author for correspondence: Dr D. Nair, D-2/2201, Vasant Kunj, New Delhi-110070, India. (Email: deepthinair2@gmail.com)