Antibiotic resistance among Salmonella enterica serovars Typhi and Paratyphi A in Pakistan (2001-2006)

Abstract

Objectives: To compare antimicrobial resistance in S. Typhi and S. Paratyphi A isolates from Pakistan. Methods: Blood samples were collected through > 175 laboratory collection points in major cities and towns across the country. The study included 3,671 S. Typhi and 1,475 S. Paratyphi A isolates (2001)(2002)(2003)(2004)(2005)(2006). Multidrug resistance (MDR) was defined as resistance to first-line agents co-trimoxazole, chloramphenicol and ampicillin. Results: In total, 79.3% S. Typhi and 59.9% S. Paratyphi A were isolated from patients under 15 years of age. During the study period, the MDR rate increased in S. Typhi (34.2 to 48.5% p<0.001), but decreased in S. Paratyphi A (44.5 to 8.6% p<0.001). Quinolone resistance (MIC>1μg/ml) increased in both S. Typhi (1.6 to 64.1% p<0.001) and S. Paratyphi A (0 to 47% p<0.001). The increase in the proportion of strains showing high level quinolone resistance (MIC >4μg/ml) was greater in S. Paratyphi A when compared to S. Typhi. Resistance to first-line drugs was higher in those <15 years of age whereas quinolone resistance was higher in older patients. Conclusion: Differences between S. Typhi and S. Paratyphi A, in terms of evolution of resistance to first-line agents and to quinolones, are evident in this population. The rapid increase in quinolone resistance in S. Paratyphi A when compared to S. Typhi is concerning and requires further study.

Is nalidixic acid screening still valid for the detection of reduced susceptibility of fluoroquinolone with SalmonellaTyphi?

“…The repeat identification and serotyping were done using standard procedures [15]. The susceptibility of all isolates to nalidixic acid was reevaluated using a 30 µg nalidixic acid disk [4] and zone diameters of ≤ 13 were considered as sensitive,, 14-18 were considered as intermediate, and ≥ 19 mm were considered as resistant [3]. The MIC of ciprofloxacin was determined using the agar dilution method.…”

“…Globally the spread of Salmonella enterica serovar Typhi (S. Typhi) strains with fluoroquinolone reduced susceptibility has become a major problem [2,3]. Current Clinical Laboratory Standards Institute (CLSI) break points for reporting fluoroquinolone susceptibility in Enterobacteriaceae do not detect these strains [4].…”

In vitro activity of azithromycin in Salmonella isolates from Pakistan

“…Studies from Pakistan indicate the incidence here may be even higher [2,3]. In addition to the high incidence of disease, Pakistan also has a high incidence of reduced quinolone susceptibility, with isolates of minimum inhibitory concentration (MIC) ≥ 1mg/L accounting for up to 64% Salmonella Typhi (S. Typhi) [3]. Within our own hospital, of the 85 Salmonella enterica isolates cultured between 2007 and 2008, 79% were resistant to nalidixic acid, a good indicator of poor response to ciprofloxacin (unpublished data).…”

“…Within our own hospital, of the 85 Salmonella enterica isolates cultured between 2007 and 2008, 79% were resistant to nalidixic acid, a good indicator of poor response to ciprofloxacin (unpublished data). Multi-drug resistance which includes resistance to ampicillin, chloramphenicol and co-trimoxazole is also high in Pakistan (45% for S. Typhi) [3].…”

Fresh Farm Vegetables as a Source of Virulent Drug Resistant Salmonella enterica

“…Resistance to traditional antibiotics like ampicillin, chloramphenicol and trimethoprim-sulfamethoxazole (Sood et al,1999) against salmonella infections has led to switching for new antibiotics like fluoroquinolones and cephalosporins which are also being ineffective (Hasan et al, 2008).…”