Presence of typical and atypical virulence genes in vibrio isolates belonging to the Harveyi clade

The study was aimed at investigating the presence of typical and atypical virulence genes in isolates belonging to the Harveyi clade (Vibrio harveyi and Vibrio campbellii).Forty-eight vibrio isolates belonging to the Harveyi clade were screened for the presence of virulence genes that are typical for these bacteria and those found in human pathogenic vibrios such as Vibrio cholerae, Vibrio parahaemolyticus and Vibrio vulnificus and aquatic pathogenic Vibrio anguillarum. The virulence genes were amplified by PCR with specific primers, and the presence further confirmed by dot blot hybridization. The virulence genes vhh, chiA, vhpA, toxR(Vh), luxR and serine protease, typical of Harveyi clade were detected in all the isolates. The haemolysin gene hlyA and the virulence regulator gene toxR(Vc) specific to V. cholerae and the V. anguillarum-specific flagellum gene (flaC) were present in some of the isolates. Challenge tests with gnotobiotic Artemia nauplii did not show any correlation between the presence of the virulence genes and virulence of the isolates.From our results, there appears a remote possibility that vibrios belonging to the Harveyi clade might acquire virulence genes from other vibrios in the aquatic environment through horizontal gene transfer.Vibrios belonging to the Harveyi clade may be an important reservoir of virulence genes of other (human pathogenic) Vibrio species in the aquatic environment. The acquisition of virulence genes by horizontal transfer might increase the ability of Harveyi clade vibrios to infect aquatic organisms by increasing their virulence to a specific host by broadening their host range. The detection of such genes may forewarn the hatchery operators about a potentially virulent pathogen and thus help to develop management measures to handle the problem of vibriosis.