Population structure and genetic diversity of Vibrio mimicus isolated from aquaculture area in Jiangsu, China

Abstract:

[Background] Vibrio mimicus, a common Gram-negative pathogen, is widely distributed in the aquatic environment and often involved in infectious diseases of aquatic animals and humans. Multilocus sequence typing (MLST) has been applied to the molecular typing of many pathogens, which allows for investigations into genetic relatedness between different strains, therefore provides insights into bacterial evolution and epidemiology. However, no report is available on the MLST of V. mimicus. [Objective] To develop a powerful MLST typing method for V. mimicus and then apply it to analyze the population structure and genetic evolution of different V. mimicus strains, and eventually provide theoretical references for the prevention and control of diseases caused by V. mimicus infection. [Methods] Seven housekeeping genes (dnaE, gyrB, mdh, recA, rpoD, pntA, and pyrH) of V. mimicus, were selected as target genes for MLST, and their conserved fragments were obtained by polymerase chain reaction (PCR) from a total of 155 V. mimicus strains isolated from the aquaculture area in Jiangsu and sequenced. All unique DNA sequences were assigned alleles, made allelic profiles, and assigned different sequence type (ST). The clonal complex and genetic evolution tree clustering of the assigned ST types were analyzed using goeBURST-1.2.1 and MEGA-X. In addition, antibiotic sensitivity of the 155 V. mimicus strains was tested using the Kirby-Bauer disk diffusion method. [Results] The 155 V. mimicus strains were divided into 56 STs, among them ST11 had the highest proportion. At the level of double locus variants (DLV), 56 STs were further divided into three clonal complexes and three monomers. Phylogenetic tree showed that 56 STs fell into three clusters (cluster I, cluster II, and cluster III). The Kirby-Bauer disk diffusion assay showed that the 155 V. mimicus strains exhibited the highest resistance to erythromycin (88.39%, 137/155) and the highest sensitivity to chloramphenicol (91.61%, 142/155). [Conclusion] The MLST method established in this study displays good resolution and can be used as a molecular typing tool for phylogeny and future epidemiological investigation of V. mimicus. Antibiotic resistance profiles suggest that florfenicol, one of antibacterial agents that approved for application, can be used for the treatment of V. mimicus infections in the aquaculture process.