Evolution and comparative genomics of pAQU-like conjugative plasmids in Vibrio species

Objectives: To investigate a set of MDR conjugative plasmids found in Vibrio species and characterize the underlying evolution process. Methods: pAQU-type plasmids from Vibrio species were sequenced using both Illumina and PacBio platforms. Bioinformatics tools were utilized to analyse the typical MDR regions and core genes in the plasmids. Results: The nine pAQU-type plasmids ranged from ~160 to 206 kb in size and were found to harbour asmany as 111 core genes encoding conjugative, replication andmaintenance functions. Eight plasmids were found to carry a typical MDR region, which contained various accessory and resistance genes, including ISCR1-blaPER-1-bearing complex class 1 integrons, ISCR2-floR, ISCR2-tet(D)-tetR-ISCR2, qnrVC6, a Tn10-like structure and others associated with mobile elements. Comparison between a plasmid without resistance genes and different MDR plasmids showed that integration of different mobile elements, such as IS26, ISCR1, ISCR2, IS10 and IS6100, into the plasmid backbonewas the keymechanismbywhich foreignresistance geneswere acquired during the evolution process. Conclusions: This study identified pAQU-type plasmids as emerging MDR conjugative plasmids among important pathogens fromdifferent origins in Asia. These findings suggest that aquatic bacteria constitute amajor reservoir of resistance genes, whichmay be transmissible to other human pathogens during food production and processing.