Isolation, identification, and resistance gene detection of Vibrio harveyi from Scophthalmus maximus

Pathogenic bacteria of Scophthalmus maximus enteritis were isolated from and identified in an aquaculture farm in Changli County, Hebei Province, China. The feasibility of rapid selection of prevention and treatment drugs via PCR technology was investigated through drug resistance phenotype analysis and drug resistance gene detection. A dominant bacterial strain was isolated from S. maximus and designated HC-1. Morphological observations, culture property investigations, and physiological-biochemical experiments were conducted, which showed that the strain was consistent with the phenotypic characteristics of Vibrio. Based on 16S rRNA sequence determination and homology analysis, HC-1 was determined to be 99.65% similar to Vibrio harveyi NR 043165.1. Therefore, the bacterium was identified as V. harveyi . The sensitivity of the V. harveyi isolate to 41 antibiotics was determined by the Kirby-Bauer method. The results showed that HC-1 was resistant to 8 agents, namely, penicillin, oxacillin, amoxicillin, ampicillin, spectinomycin, azithromycin, florfenicol, and carbenicillin. The antimicrobial resistance gene analysis results showed that tem , ant (3˝)-I and tet A are carried by the chromosome of the strain and the plasmid, while sul 1 is carried by the chromosome of the strain but not the plasmid. In contrast, floR is carried only by the plasmid but not by the chromosome. van A, qnr A, and mef A are not carried by the plasmid or chromosome of the strain. Although the resistant phenotype of the strains is regulated by resistance genes, the relationship between the phenotype and genotype should be revealed by numerous databases. To accelerate the speed of treatment selection, it is necessary to apply PCR technology to detect resistance genes to replace drug sensitivity testing. These results provide useful information for further understanding the antimicrobial resistance factors and treatment of bacterial disease in S. maximus.