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

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 (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 microg/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.

Salmonella enterica serovar Typhi and S. Paratyphi A: need to expand the QRDR region?

“…Of the 163 E. coli available sequences in the GenBank databases, we found in all instances Gly 31 , Val 44 , Asp 72 , and Lys 76 . The discrepancies between our results and those reported by Capoor and colleagues [1,6] could be caused by different numbering of the residues because the precursor GyrA protein may be processed into a signal peptide and a functional enzyme. However, this is contradicted by the numbering of the residues, Met 52 , Ser 83 , and Asp 87 , which is in accordance with an unprocessed precursor GyrA protein.…”

“…are : Typhi CT18, NC_003198 ; Typhi Ty2, NC_004631 ; Typhimurium, NC_003197 ; Dublin, NC_011205 ; Javiana, NZ_ABEH02000005 ; Kentucky, NZ_ABEI01000001 ; Tennessee, ACBF01000027 ; 62z4,z23-, NC_010067 ; Virchow, NZ_ABFH02000001 ; Gallinarum, NC_011274 ; Schwarzengrund, NC_011094 ; Typhi 2114, AM283471 ; Choleraesuis, NC_006905 ; E. coli K-12, NC_000913. [1] form the basis of their conclusion on an expansion of QRDR, but owing to the dubious positions of some of the described substitutions as shown in this letter, this conclusion may need a reassessment.…”

“…Resistance to nalidixic acid is often mediated by substitutions in position Ser 83 or Asp 87 of GyrA while resistance to both nalidixic acid and ciprofloxacin frequently is the result of substitutions in both positions [3,4]. The positions 83 and 87 are parts of the so-called quinolone resistance-determining region (QRDR) which has been defined by Yoshida and coworkers to cover the region between position 67 and 106 of GyrA [5], but Capoor and colleagues have proposed a highly relevant expansion of QRDR [1]. We also used Salmonella (taxid : 590) as the optional organism.…”

“…Regarding the Glu 133 pGly substitution [1], it is correct that Glu is the prevalent residue in position Fig. 1.…”

Molecular Typing and Resistance Analysis of Travel-Associated Salmonella enterica Serotype Typhi

“…However, there has been a global increase in nalidixic acid (NAL)-resistant strains causing decreased ciprofloxacin susceptibility (DCS) (1,7,22). This DCS may lead to longer fever clearance times and frequent treatment failures (6,7,40). Quinolone resistance in Salmonella spp.…”