[Study on the source tracing and molecular characteristics of pathogenic bacteria of an outbreak of vibrio cholerae O139 serogroup].

This study aimed to analyze the epidemiological and etiological molecular characteristics of an outbreak of cholera caused by Vibrio cholerae serogroup O139, so as to provide a reference for the handling of cholera outbreaks. Case-by-case investigation and epidemiological analysis of the outbreak were carried out. Feces or anal swabs of the exposed population and specimens from the suspected links related to the epidemic were collected for isolation, culture, nucleic acid detection, and drug resistance analysis of Vibrio cholerae. The isolates were subjected to whole-genome sequencing using a next-generation sequencing platform. The sequencing data were used to predict virulence genes and drug resistance genes. The core genome multilocus sequence typing (cgMLST) and core genome single-nucleotide polymorphism (cgSNP) were analyzed by comparing with the genomic sequences of local Vibrio cholerae isolates and those of Vibrio cholerae serogroup O139 downloaded from NCBI. Epidemiological investigation showed that this cholera outbreak was highly associated with a local wedding banquet. The outbreak was caused by Vibrio cholerae serogroup O139 (ctxAB+) strain. There were 11 infected individuals, including 2 cases and 9 carriers. The drug resistance phenotype of the isolates showed resistance to tetracycline, nalidixic acid, streptomycin, polymyxin E, and azithromycin, intermediate resistance to chloramphenicol, and sensitivity to other drugs. Gene prediction of the 11 isolates showed that they all carried important virulence factors such as ctxA, ctxB, tcpA, zot, ace, msh, rtx, and hlyA, as well as drug resistance genes against fluoroquinolones, aminoglycosides, β-lactams, macrolides, sulfonamides, and tetracyclines. The MLST typing was ST69. Both cgMLST and cgSNP analyses showed that the isolates from this outbreak formed an independent genetic branch and had no genetic relationship with local Vibrio cholerae isolates. Based on the above, this outbreak was caused by Vibrio cholerae O139 serogroup of sequence type 69 (ST69), carrying complete core virulence factors (ctxAB+, tcpA+, etc.), and showed strong epidemiological association with the wedding banquet (particularly soft-shelled turtle consumption). Genomic analysis revealed it formed an independent clonal cluster unrelated to local historical strains. Most infections manifested as asymptomatic carriage, posing substantial risks for secondary transmission. The high carrier ratio underscores the importance of enhanced surveillance. This study recommends strengthening regulatory monitoring of aquatic foods (particularly high-risk items like soft-shelled turtles) and improving hygiene management of banquet gatherings in both urban and rural areas, implementing multi-source interventions to curb cholera outbreaks.