Pathogenesis, virulence factors and virulence regulation of vibrios belonging to the <i>Harveyi</i> clade

Abstract The Harveyi clade or core group of the Vibrio genus includes both pathogenic and non‐pathogenic bacteria. Some of the species belonging to the clade, such as Vibrio harveyi , Vibrio alginolyticus , Vibrio campbellii and Vibrio parahaemolyticus , include serious pathogens of aquatic organisms. Importantly, within these species, some strains are pathogenic, whereas others are not. Other members of the clade, such as Vibrio natriegens and Vibrio mytili are reported to be non‐pathogenic. As bacteria belonging to the Harveyi clade show a high diversity with respect to virulence and as the virulent members cause high mortalities in the aquaculture sector, it is important to understand which gene products are responsible for the pathogenicity of the bacteria and how expression of these virulence factors is regulated. This knowledge will ultimately allow for the development of biocontrol measures that aim to reduce the severe losses that are currently faced in the aquaculture sector as a result of vibriosis. In this review, we discuss the pathogenesis of bacteria belonging to the Harveyi clade, their impact on the aquaculture sector, the virulence factors that are involved in pathogenicity and their regulation.