Genomic characterization of clinical and environmental Vibrio cholerae O1 and O139 isolates in Jiaxing, China, with identification of a ctx-positive O139 strain harboring an IncC plasmid.

INTRODUCTION

Vibrio cholerae serogroups O1 and O139 are responsible for epidemic and pandemic cholera. Although the pathogenic potential and genomic diversity of V. cholerae strains have been extensively studied in endemic regions, limited genomic data are available for more developed regions such as Jiaxing.

METHODS

In this study, 15 V. cholerae O1 and O139 isolates (eight clinical and seven environmental) collected between 2021 and 2024 were analyzed. Antimicrobial susceptibility testing (AST) was performed, and whole-genome sequencing was conducted. Comparative genomic analyses were used to characterize antimicrobial resistance (AMR) determinants, virulence-associated genes, and population structure. Core genome multilocus sequence typing (cgMLST) was applied to assess genetic relatedness.

RESULTS

All strains were susceptible to ciprofloxacin, trimethoprim-sulfamethoxazole, tigecycline, and amikacin. Elevated MIC values were observed for colistin; however, no interpretive criteria are available for V. cholerae. By contrast, high resistance rates were observed for streptomycin, chloramphenicol, and azithromycin. Resistance genes, including qnr, tet, mph, and sul, were widely distributed, while bla genes were absent. One clinical O139 strain, VC0827, was found to harbor the ctxAB genes, a truncated CTX prophage, and an IncC plasmid (pVC0827), which carried several antimicrobial resistance genes including tet(A/B/M), flor, sul2, and msr(E). cgMLST analysis revealed three main clusters; VC0827 clustered closely with seventh-pandemic reference strains and shared sequence type ST69. The observed gene duplications (e.g., ace and zot) in VC0827 may enhance its toxigenic potential.

CONCLUSION

This study highlights the genomic diversity and resistance profiles of V. cholerae in Jiaxing. The identification of a potentially virulent, multidrug-resistant O139 strain underscores the need for continuous genomic surveillance to monitor the emergence of toxigenic lineages and horizontal gene transfer.