Abstract
Background: Antimicrobial resistance in enteric fever is a major therapeutic challenge and there is a need to monitor the pattern of resistance to the antityphoidal agents and detection of molecular mechanisms of resistance.The study was designed to monitor the antimicrobial susceptibility of Salmonella enterica serovars Typhi and Paratyphi A isolated from patients of enteric fever during 2014 to 2019 and detection of antimicrobial resistance mechanisms to quinolones. Methods and materials: Total 281 strains isolated from January 2014 to September 2019 were selected for the study. Antimicrobial susceptibility was done as per CLSI guidelines (2019) for amoxicillin, chloramphenicol, co-trimoxazole, ciprofloxacin, ceftriaxone and azithromycin. Minimum inhibitory concentration (MIC) determination for ciprofloxacin, ceftriaxone and azithromycin were done by E-Test method according to manufacturer's (ABs Biodisk, Sweden) instructions. DNA sequencing was done for gyrA, gyrB, parC and parE genes to find mutations in quinolone resistance determining region (QRDR). Results: Out of total 281 strains included in the study 214 (76.2%) were S. Typhi and 67 (23.8%) were S. Paratyphi A. As per CLSI 2019, antimicrobial susceptibility for chloramphenicol, ampicillin and cotrimoxazole was 0.7% (2/281), 1.42% (4/281) and 1.06% (3/281) respectively. Only 6/214 (2.8%) were susceptible for S. Typhi and no strain was found to be susceptible in S. Paratyphi A. Azithromycin susceptibility was 100% in S. Typhi, for S. Paratyphi there is no breakpoint available. Ciprofloxacin MIC50 and MIC90 values found to be 0.25 μg/mL and 1 μg/mL in S. Typhi and 0.5 μg/mL and 6 μg/mL in S. Paratyphi A. Ceftriaxone MIC50 and MIC90 values found to be 0.023 μg/mL and 0.5 μg/mL in both S. Typhi and S. Paratyphi A. For azithromycin MIC50 and MIC90 were 2 μg/mL and 6 μg/mL for S. Typhi and 4 μg/mL and 12 μg/mL for S. Paratyphi A respectively. All quinolone resistance strains had mutations in QRDR of gyrA and parC genes. Conclusion: Ciprofloxacin is no longer a drug of choice for treatment of enteric fever in India. Although susceptibility to ceftriaxone is 100% but MIC is creeping towards resistance. Azithromycin can be a promising treatment option for uncomplicated enteric fever.
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