Abstract
This study aimed to determine the drug susceptibility patterns and genetic elements related to drug resistance in isolates of Salmonella enterica serovar Typhi (S. Typhi) from the Faisalabad region of Pakistan. The drug resistance status of 80 isolates were evaluated by determining antimicrobial susceptibility, MICs, drug resistance genes involved, and the presence of integrons. Nalidixic acid resistance and reduced susceptibility to ciprofloxacin were also investigated by mutation screening of the gyrA, gyrB, parC, and parE genes. Forty-seven (58.7%) isolates were multidrug resistant (MDR). Among the different resistance (R) types, the most commonly observed (13/80) was AmChStrTeSxtSmzTmp, which is the most frequent type observed in India and Pakistan. The most common drug resistant genes were blaTEM-1, cat, strA-strB, tetB, sul1, sul2, and dfrA7. Among the detected genes, only dfrA7 was found to be associated in the form of a single gene cassette within the class 1 integrons. MIC determination of currently used drugs revealed fourth-generation gatifloxacin as an effective drug against multidrug-resistant S. Typhi, but its clinical use is controversial. The Ser83→Phe substitution in gyrA was the predominant alteration in nalidixic acid-resistant isolates, exhibiting reduced susceptibility and increased MICs against ciprofloxacin. No mutations in gyrB, parC, or parE were detected in any isolate.
Highlights
This study aimed to determine the drug susceptibility patterns and genetic elements related to drug resistance in isolates of Salmonella enterica serovar Typhi
Sulfonamide was the least active drug (73.7% resistance), whereas the most active antimicrobial agent was cefoparazone/sulbactam (2.5% resistance)
Nalidixic acid (NA) and ciprofloxacin were included in the quinolone group for disk diffusion testing
Summary
Methodology: The drug resistance status of 80 isolates were evaluated by determining antimicrobial susceptibility, MICs, drug resistance genes involved, and the presence of integrons. Nalidixic acid resistance and reduced susceptibility to ciprofloxacin were investigated by mutation screening of the gyrA, gyrB, parC, and parE genes. Conclusions: MIC determination of currently used drugs revealed fourth-generation gatifloxacin as an effective drug against multidrugresistant S. The Ser83→Phe substitution in gyrA was the predominant alteration in nalidixic acidresistant isolates, exhibiting reduced susceptibility and increased MICs against ciprofloxacin. Quinolones/fluoroquinolones and third-generation cephalosporins have emerged as current front-line drugs against typhoid. Resistance against nalidixic acid has emerged rapidly in recent years [2]
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