Ecology, virulence factors and global spread of vibrio parahaemolyticus

Abstract

Vibrio parahaemolyticus is part of the autochthonous microflora in estuarine and coastal marine environments and is associated with water, sediment and various aquatic animals ranging from tiny zooplankton to marine mammals. The ecology of this organism is affected by temperature, salinity, turbidity, and the presence of zooplankton, crustaceans and molluscs. Most environmental strains are non-pathogenic to man and human pathogenic strains are characterized by the ability to produce a thermostable direct haemolysin (TDH) and tdh-related haemolysin (TRH). The tdh and trh genes are present in genomic islands that have been possibly acquired by V. parahaemolyticus by lateral gene transfer. Strains of V. parahaemolyticus causing acute hepatopancreatic necrosis disease (AHPND) harbour a 70 kb conjugative plasmid carrying pirA and pirB genes encoding a binary Photorhabdus insect-related toxin A and B (PirAB). Genetically diverse strains of V. parahaemolyticus isolated in Asia seem to have acquired the 70 kb plasmid, while Central American AHPND strains can be distinguished from Asian strains based on PCR amplification of TN-3-like transposon. All AHPND-causing strains tested so far lack virulence factors associated with human pathogenic strains, suggesting that risk to human health due to these strains is negligible. Bacteriophage therapy has shown potential for management of AHPND.