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Chapter 24 : Vibrio parahaemolyticus
Category: Environmental Microbiology
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Vibrio parahaemolyticus, a gram-negative marine bacterium, causes seafood-borne gastroenteritis in humans. The major source of V. parahaemolyticus infection is contaminated seafood or seafood products. The whole genome sequence of the clinical V. parahaemolyticus strain RIMD2210633 was recently reported. The most notable finding in relation to the pathogenicity of V. parahaemolyticus was the presence of two sets of genes for the type III secretion system (TTSS) in the genome. TTSS is an apparatus of gramnegative pathogenic bacteria used to secrete and translocate virulence factor proteins into the cytosol of target eukaryotic cells. To determine whether the two sets of the TTSS genes identified in the genome of V. parahaemolyticus are functional, a series of mutant strains from strain POR-1 was constructed. POR-1 was used as the parent strain for further mutant construction to exclude the influence of thermostable direct hemolysin (TDH) production on bacterial phenotypes. To examine the role of TTSS1 and TTSS2, specific genes were disrupted using inframe deletions by homologous recombination with the positive selection suicide vector pYAK1. The genes thus disrupted were vcrD1 and vcrD2, each encoding an inner membrane protein; vscC1 and vscC2, each encoding an outer membrane protein; and vscN1 and vscN2, each encoding a cytoplasmic protein, of the TTSS apparatus. Genome sequencing of V. parahaemolyticus and subsequent studies have shed light on hitherto unknown aspects of the pathogenicity of this organism. Both of the two sets of TTSS in KP-positive V. parahaemolyticus are functional and are involved in distinct phenotypes.
Location of the TTSS genes in the genome of V. parahaemolyticus strain RIMD2210663. Two sets of the genes for the TTSS were found by genome sequencing (Makino et al., 2003). One set (TTSS1) was located on chromosome 1, and the other (TTSS2) was identified within the PAI region on chromosome 2.
Comparison of the TTSS genes in V. parahaemolyticus and other bacteria