Genomic characteristics of clinical non-toxigenic Vibrio cholerae isolates in Switzerland: a cross-sectional study.

Abstract

Although non-toxigenicVibrio choleraelack thectxABgenes encoding cholera toxin, they can cause diarrhoeal disease and outbreaks in humans. In Switzerland,V. choleraeis a notifiable pathogen and all clinical isolates are analysed at the National Reference Laboratory for Enteropathogenic Bacteria and Listeria. Up to 20 infections are reported annually. In this study, we investigated the population structure and genetic characteristics of non-toxigenicV. choleraeisolates collected over five years. V. choleraeisolates were serotyped and non-toxigenic isolates identified using actxA-specific PCR. Following Illumina whole-genome sequencing, genome assemblies were screened for virulence and antibiotic resistance genes. Phylogenetic analyses were performed in the context of 965 publicly availableV. choleraegenomes. Out of 33V. choleraeinfections reported between January 2017 and January 2022 in Switzerland, 31 were caused byctxA-negative isolates. These non-toxigenic isolates originated from gastrointestinal (n = 29) or extraintestinal (n = 2) sites. They were phylogenetically diverse and belonged to 29 distinct sequence types. Two isolates were allocated to the lineage L3b, actxAB-negative buttcpA-positive clade previously associated with regional outbreaks. The remaining 29 isolates were placed in lineage L4, which is associated with environmental strains. Genes or mutations associated with reduced susceptibility to the first-line antibiotics fluoroquinolones and tetracyclines were identified in 11 and 3 isolates, respectively. One isolate was predicted to be multidrug resistant. V. choleraeinfections in Switzerland are rare and predominantly caused by lowly virulentctxAB-negative andtcpA-negative strains. AsV. choleraeis not endemic in Switzerland, cases are assumed to be acquired predominantly during travel. This assumption was supported by the phylogenetic diversity of the analysed isolates.