Reduced Susceptibility to Ciprofloxacin andgyrAGene Mutation in North Indian Strains ofSalmonella entericaSerotype Typhi and Serotype Paratyphi A

Abstract

The emergence of reduced susceptibility to ciprofloxacin among Salmonella enterica serotype Typhi and serotype Paratyphi A leading to clinical failure of treatment poses a great therapeutic challenge. The mechanism of fluoroquinolone resistance in clinical isolates of S. Typhi and S. Paratyphi A is not very well documented. The present study was carried out with the objective of molecular characterization of reduced quinolone susceptibility amongst the strains of S. Typhi and S. Paratyphi A isolated from the patients with enteric fever during January, 2000, to April, 2003, in a North Indian hospital. A total of 422 culture-positive cases of enteric fever were reported to the hospital during the period of study, of which S. Typhi was isolated from 350 cases and S. Paratyphi A from 72 cases. The antimicrobial susceptibility of these strains was determined by disk diffusion and agar dilution method according to NCCLS guidelines, and E-test method. A total of 140 randomly selected strains, isolated during the years 1993-1999, that were available from the laboratory stocks were also studied to compare with the present strains. To study the quinolone susceptibility, the strains were divided into nalidixic acid sensitive (NAS), nalidixic acid intermediate resistant, (NAI) and nalidixic acid resistant (NAR) on the basis of susceptibility to nalidixic acid. Clinical history was available from 174 patients, of which 93 needed hospitalization due to severe disease. Of these, 82 patients were infected with NAR strains and 22 patients had a documented evidence of clinical failure to ciprofloxacin therapy. The patients infected with NAR strains were younger and had a significantly longer duration of fever (p value < 0.05) than those infected with NAS strains. It was observed that the proportion of NAR strains increased gradually over the years. These strains had a significantly higher range of MIC of ciprofloxacin (0.023-1.0 microg/ml) as compared to the NAS strains (0.002-0.125 microg/ml) (p value < 0.05). The sequencing of quinolone resistance determining region (QRDR) of the gyrA gene showed the presence of mutation at either Ser 83 or at Asp 87 in all the NAR and NAI strains. None of the NAS strains had a mutation, suggesting that the gyrA gene mutation is sufficient to confer resistance to nalidixic acid and reduced susceptibility to ciprofloxacin. This mutation, although phenotypically expressed as decreased susceptibility to ciprofloxacin, goes undetected by the disk diffusion method using the present NCCLS guidelines. Hence, it can increase morbidity and mortality due to delay in appropriate antibiotic treatment.

Salmonella Typhi: A Changing Sensitivity Pattern: Reply

“…The sensitivity of S paratyphi A to chloramphenicol, ampicillin, septran, gentamicin, ciproflox and cephalexin was 100%, 81%, 100%, 72% and 100% respectively. A similar pattern of increasing sensitivity to chloramphenicol and resistance to ciproflox is also being reported in other Indian studies (2,3). A rotation of antibiotics and usage of antibiotics based on sensitivity patterns of S typhi will help in preventing a reemergence of outbreaks of MDRST (multi drug resistant S typhi).…”

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

“…Other researchers from India have reported incidences varying from 47% to 100% [13,18,19]. However, in developed countries, NARST incidence has been reported to be much lower (0%-17%) [17,20].…”

“…Since 2000, a re-emergence of sensitivity to the classical first-line agents has been observed, due to their restricted use in the "ciprofloxacin era" of the 1990s. There has been a concomitant decrease in susceptibility to ciprofloxacin and nalidixic acid in this region [13,18,19].…”

“…Single 87 Asp→Asn substitution in gyrA of two NARST strains is a common association reported with NARST [3,12,20]. 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].…”

“…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]. We examined the incidence of NARST, decreased susceptibility to ciprofloxacin and made molecular analyses of these strains.…”