Pathogenesis, virulence factors and virulence regulation of vibrios belonging to the Harveyi 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

Bacterial diseases in marine bivalves

“…Additional species have been added to this clade: V. azureus, V. owensii, V. communis and V. sagamiensis (Hoffmann et al, 2012). Members of this clade have been responsible for mortality outbreaks worldwide involving both fish and shellfish Saulnier et al, 2010;Ruwandeepika et al, 2012).…”

“…Virulence factors -Species of this clade produce several virulence factors reported elsewhere (see Ruwandeepika et al, 2012). Briefly, these, which vary among taxa, can be grouped in five types: (i) production of adhesion factors including adhesion to mucus, presence of pili, and chitinase; (ii) production of a variety of extracellular polysaccharides and biofilm formation derived from some of them, (iii) production of lytic proteins mainly hemolysins and proteases, (iv) siderophores and iron acquisition, (e.g.)…”

Indole signalling and (micro)algal auxins decrease the virulence of Vibrio campbellii, a major pathogen of aquatic organisms

“…Vibrio campbellii and related species belonging to the Harveyi clade of vibrios, are marine Gram‐negative bacteria that can infect a wide range of wild and cultured aquatic organisms (both vertebrates and invertebrates), leading to significant losses in the aquaculture industry worldwide (Austin and Zhang, ; Ruwandeepika et al ., ; Dong et al ., ). Despite their role as major pathogens of marine animals, the pathogenicity mechanisms of these bacteria are not yet fully understood.…”

Quorum sensing is required for full virulence of Vibrio campbellii towards tiger grouper (Epinephelus fuscoguttatus) larvae

“…Vibrio spp. are major pathogens in the intensive rearing of molluscs (Romalde, Dieguez, Lasa, & Balboa, ), crustaceans (Manilal et al., ) and finfishes (Austin & Austin, ; Pietrak, Molloy, Bouchard, Singer, & Bricknell, ) in various marine and brackish habitats, and Vibrio campbellii is amongst the most important pathogens in aquaculture (Ruwandeepika et al., ). Several studies have investigated pathogenicity mechanisms of these bacteria in order to understand the infection process and to develop novel therapies based on this knowledge.…”