Antimicrobial susceptibility and virulence profile of <i>Vibrio cholerae</i> from Delhi, India: effect of floods on epidemiology

BACKGROUND: Cholera remains endemic in India, with outbreaks frequently intensifying during the monsoon due to flooding and disruption of water and sanitation systems. Recent floods in Delhi have raised concerns regarding changing epidemiology, antimicrobial resistance (AMR) and circulation of virulent Vibrio cholerae lineages. METHODS: This was a retrospective analysis of V. cholerae isolates obtained from stool samples at a tertiary care hospital in Delhi from May 2018 to December 2024. Isolates were identified by conventional methods and serotyping. Antimicrobial susceptibility testing was conducted using disk diffusion as per Clinical and Laboratory Standards Institute guidelines. Molecular characterization was performed for virulence genes (ctxB, tcpA, rtxA) and ctxB sequencing. RESULTS: Eighty-five V. cholerae isolates were analysed, predominantly affecting children (78.8%), with a post-monsoon peak. All isolates belonged to serogroup O1, serotype Ogawa, El Tor biotype. High resistance was observed to co-trimoxazole (77.6%) and ampicillin (55.3%), with moderate resistance to ciprofloxacin (24.7%); all isolates remained susceptible to azithromycin and ceftazidime. Virulence genes were detected in most sequenced isolates and ctxB sequencing revealed mutations consistent with contemporary epidemic lineages. CONCLUSIONS: The study demonstrates persistent circulation of toxigenic V. cholerae O1 Ogawa strains in Delhi, with seasonal clustering following floods and evolving AMR patterns. Continuous surveillance integrating phenotypic and molecular data is essential to guide therapy and strengthen cholera control in flood-prone urban settings.