Prevalence of Mutations within the Quinolone Resistance-Determining Region of gyrA , gyrB , parC , and parE and Association with Antibiotic Resistance in Quinolone-Resistant Salmonella enterica

Abstract

Salmonella enterica isolates (n ‫؍‬ 182) were examined for mutations in the quinolone resistance-determining region of gyrA, gyrB, parC, and parE. The frequency, location, and type of GyrA substitution varied with the serovar. Mutations were found in parC that encoded Thr57-Ser, Thr66-Ile, and Ser80-Arg substitutions. Mutations in the gyrB quinolone resistance-determining region were located at codon Tyr420-Cys or Arg437-Leu. Novel mutations were also found in parE encoding Glu453-Gly, His461-Tyr, Ala498-Thr, Val512-Gly, and Ser518-Cys. Although it is counterintuitive, isolates with a mutation in both gyrA and parC were more susceptible to ciprofloxacin than were isolates with a mutation in gyrA alone.The four most common nontyphoidal Salmonella enterica serovars isolated from humans in England and Wales in 1999 were Enteritidis (57%), Typhimurium (18%), Virchow, and Hadar (14). In the last decade, the numbers of isolates of these serovars with decreased susceptibility to ciprofloxacin (MIC, Ն1 g/ml) have increased (12). In 2000, 52% of the S. enterica serovar Virchow isolates tested exhibited decreased susceptibility to ciprofloxacin (12). It is postulated that many of these isolates have arisen in animals after fluoroquinolone exposure and have been transferred to humans via the food chain (11).In salmonellae, where DNA gyrase is the primary target of quinolone action, a single point mutation in the quinolone resistance-determining region (QRDR) of gyrA can mediate resistance to the nonfluorinated quinolone nalidixic acid and reduced susceptibility to fluoroquinolones such as ciprofloxacin, e.g., an MIC of 0.25 g/ml (10). Mutations in the gyrB and topoisomerase IV genes parC and parE are considered rare in salmonellae (6,7,9,11). It was hypothesized that those isolates with decreased susceptibility harbored a single mutation in gyrA, whereas resistant isolates would contain two or more mutations in gyrA and/or gyrB and/or parC and/or parE.S. enterica isolates (n ϭ 182; 156 from animals, 18 from humans, and 18 from the environment) representative of the 25 serotypes typically isolated between 1997 and 2000 were obtained from the Enteric Bacteria Reference Laboratory of the Veterinary Laboratories Agency. Because of the recent debate about the breakpoint concentration of ciprofloxacin (1,8), isolates resistant to Ն0.12 g of ciprofloxacin per ml were investigated. Isolates were serotyped by a microagglutination method (13) and, where appropriate, were phage typed (15). All isolates were from geographically and temporally distinct samples. Isolates were also analyzed by pulsed-field gel electrophoresis, which confirmed that no clones were examined.

Molecular Analysis of Fluoroquinolone-resistantSalmonellaParatyphi A Isolate, India

“…For gyrA from nalidixic acid–resistant Salmonella isolates, 2 mutations are most frequently observed in clinical isolates: Ser83→Phe and Ser83→Tyr ( 8 , 9 , 11 ). The association with resistance of mutations seen in parC , however, is less clear ( 12 ).…”

Mecanismos de resistência às quinolonas em Salmonella spp.

“…A maior parte das cepas com esta característica surgiu inicialmente em animais expostos a fluoroquinolonas. Posteriormente, essas cepas foram transmitidas aos seres humanos via cadeia alimentar (EAVES et al, 2004;ESCRIBANO, et al, 2004).…”

Salmonella enterica serovar typhi: molecular analysis of strains with decreased susceptibility and resistant to ciprofloxacin in india from 2001-2003

“…Nonetheless, the single mutations seen in a NARST isolate at 76 Asp→Asn were hitherto unknown [3,12,13,20]. However, there is a single report of 72 Phe→Tyr substitution in S. Seftefberg, in combination with 83 Ser→Phe [10].…”

“…There have been isolated reports of ciprofloxacin resistance in S. Typhi, from India [6][7][8] and elsewhere [9]. Nonetheless, high-level fluoroquinolone resistance in non-enteric fever salmonellae is frequent, with MICs ranging from 16-64 μg/mL [10][11][12]. Molecular analysis studies of fluoroquinolone resistance or decreased susceptibility in clinical isolates of S. Typhi are relatively scarce from India [6,13].…”