Re-emergence of Conventional Drug Susceptibility Amid Persistent Fluoroquinolone Resistance in Enteric Fever.

Background Fluoroquinolone resistance among Salmonella isolates causing enteric fever has emerged as a major therapeutic challenge in India. The present study evaluated the clinical profile, antimicrobial susceptibility patterns and genomic mechanisms of fluoroquinolone resistance among Salmonella isolates from a tertiary care centre in Eastern India. Methods This retrospective observational study included 30 patients with blood culture-confirmed enteric fever between January 2023 and December 2025. Blood cultures were processed using the BacT/ALERT system (bioMérieux, France), and isolates were identified by standard biochemical tests and VITEK 2 Compact (bioMérieux). Antimicrobial susceptibility testing (AST) was performed using the Kirby-Bauer disk diffusion method as per the Clinical and Laboratory Standards Institute (CLSI) guidelines. Bacterial whole-genome sequencing (WGS) was performed for two representative isolates, and resistance determinants were identified using NCBI databases. Results The median age of patients was 14.75 years with male predominance (73.3%). Salmonella Typhi accounted for 56.7% of isolates, followed by Salmonella Paratyphi A (43.3%). Fluoroquinolone resistance was observed in 63.3% of isolates. However, all isolates remained susceptible to ceftriaxone, azithromycin, chloramphenicol, cotrimoxazole and carbapenems. WGS revealed gyrA (S83F, D87N), parC (S80I) and qnrS1-mediated resistance in one isolate, while another demonstrated efflux-mediated resistance without quinolone resistance-determining region (QRDR) mutations. Conclusion The study highlights persistent fluoroquinolone resistance among Salmonella isolates causing enteric fever, alongside preserved susceptibility to cephalosporins, azithromycin and conventional first-line drugs. Continuous antimicrobial surveillance and genomic monitoring are essential to guide effective therapy and antimicrobial stewardship.