Vibrio repeats (VXRs) play a role in horizontal dissemination of sedentary chromosomal integron-associated antibiotic resistance genes across Vibrio species

Abstract

Sedentary chromosomal integrons (SCIs) are large integrons that harbor extensive arrays of gene cassettes and constitute major reservoirs of bacterial genetic diversity. In Vibrio, SCI cassettes are flanked by species-associated attC repeats, here referred to as Vibrio species repeats (VXRs). Although SCIs have been proposed as ancestral sources of antibiotic resistance genes (ARGs), the extent to which SCI-associated ARGs are exchanged among Vibrio species remains poorly understood. To investigate the dynamics of SCI-associated ARGs, we analyzed 37,812 genomes representing 181 Vibrio species. Using VXR mapping, comparative phylogenetics, and genome screening, we identified 8,679 putative ARG cassettes distributed across 8,517 genomes from 11 species. Despite the diversity of VXRs identified in SCIs, ARG cassettes were predominantly associated with a small subset of related VXRs shared among phylogenetically distant species, suggesting horizontal transfer of ARG-associated cassettes across the genus. Comparative analyses further suggested that members of the Cholera clade may act as potential sources of SCI-associated ARG dissemination. Five major ARG families were identified within SCIs, including catB, qnrVC, bla_CARB, dfrA, and vatF, some of which displayed phylogenetic patterns consistent with interspecies transfer. Functional characterization of a SCI-associated qnrVC4 cassette from Vibrio mimicus confirmed its ability to confer reduced susceptibility to ciprofloxacin in a heterologous host. Together, our findings indicate that a conserved subset of VXR backbones, mainly from the Cholera clade, plays a role in ARG dissemination across Vibrio species, highlighting SCIs as active reservoirs contributing to the emergence and spread of antimicrobial resistance.