Comparison of 16SrDNA and toxR genes as targets for detection of Vibrio anguillarum in Dicentrarchus labrax kidney and liver

Vibrio anguillarum is a pathogen that causes high mortality in marine and freshwater fish. The aim of this study was to develop a real-time PCR assay for identification and quantification of V. anguillarum in fish tissue. The assay was carried out using two target genes, 16SrDNA and toxR, to evaluate the influence of differences in the operon copy number in quantitative assessment, both in pure cultures of V. anguillarum serovar O1 (strain 975/I), as a reference, and in the liver and kidney of a sea bass (Dicentrarchus labrax) specimen. Real-time PCR analysis showed high specificity for both target genes, with a detection limit of approximately 1-10 bacterial cells per reaction in pure culture and 10/100 V. anguillarum cells per reaction in fish tissue, which corresponds to 2 × 102/2 × 103 cells g−1 fish tissue. Moreover, both genes showed high specificity but differing sensitivity due to the different operon copy number; as a result, it is possible to target the high copy number gene to improve sensitivity. Our results suggest that the protocol we tested can be used as a sensitive and specific molecular method for the detection of the fish pathogen V. anguillarum in fish tissue.