Contribution of Vibrio parahaemolyticus Virulence Factors to Cytotoxicity, Enterotoxicity, and Lethality in Mice

Abstract

Vibrio parahaemolyticus, one of the human-pathogenic vibrios, causes three major types of clinical illness: gastroenteritis, wound infections, and septicemia. Thermostable direct hemolysin (TDH) secreted by this bacterium has been considered a major virulence factor of gastroenteritis because it has biological activities, including cytotoxic and enterotoxic activities. Previous reports revealed that V. parahaemolyticus strain RIMD2210633, which contains tdh, has two sets of type III secretion system (T3SS) genes on chromosomes 1 and 2 (T3SS1 and T3SS2, respectively) and that T3SS1 is responsible for cytotoxicity and T3SS2 is involved in enterotoxicity, as well as in cytotoxic activity. However, the relative importance and contributions of TDH and the two T3SSs to V. parahaemolyticus pathogenicity are not well understood. In this study, we constructed mutant strains with nonfunctional T3SSs from the V. parahaemolyticus strain containing tdh, and then the pathogenicities of the wild-type and mutant strains were evaluated by assessing their cytotoxic activities against HeLa, Caco-2, and RAW 264 cells, their enterotoxic activities in rabbit ileal loops, and their lethality in a murine infection model. We demonstrated that T3SS1 was involved in cytotoxic activities against all cell lines used in this study, while T3SS2 and TDH had cytotoxic effects on a limited number of cell lines. T3SS2 was the major contributor to V. parahaemolyticus-induced enterotoxicity. Interestingly, we found that both T3SS1 and TDH played a significant role in lethal activity in a murine infection model. Our findings provide new indications that these virulence factors contribute to and orchestrate each distinct aspect of the pathogenicity of V. parahaemolyticus.Vibrio parahaemolyticus is a Gram-negative halophilic bacterium that inhabits estuarine and coastal waters and can be isolated from seafood (6,7,9). It causes acute gastroenteritis in humans after they consume contaminated raw or undercooked seafood. Although this microorganism is better known for causing gastroenteritis, it also can cause wound infections and septicemia (5,23,36).Most clinical isolates of V. parahaemolyticus from patients with diarrhea show ␤-hemolysis on Wagatsuma agar (37). This phenomenon is known as the Kanagawa phenomenon (KP) and is considered a good marker to distinguish between pathogenic and nonpathogenic V. parahaemolyticus strains (25, 37). Thermostable direct hemolysin (TDH), which is responsible for the KP (28, 43), has multiple biological activities, including hemolysis, enterotoxicity, cytotoxicity, and cardiotoxicity (11-13, 26, 29, 32, 34, 38). For this reason, TDH has been considered a major virulence factor of V. parahaemolyticus.Whole-genome sequencing of a KP-positive V. parahaemolyticus strain revealed that this strain contains two sets of gene clusters for the type III secretion system (T3SS), T3SS1 and T3SS2, one on each of its two chromosomes (21). T3SS gene clusters have been detected in numerous Gram-negative animal and plant pathogens, wh...

Biochemical, Serological, and Virulence Characterization of Clinical and Oyster Vibrio parahaemolyticus Isolates

“…Together, tdh and trh are widely considered the predominant indicators of strain virulence in V. parahaemolyticus (26,37,38). This is substantiated by the prevalence of tdh and/or trh in clinical V. parahaemolyticus isolates and the infrequent detection of these virulence markers in food and environmental samples (9,27,28,35,40).Investigations of the in vitro virulence effects of the TDH have demonstrated its involvement in cytotoxicity, hemolytic activity, and mouse lethality (14,22). Although few studies have directly addressed the effects of TRH production on pathogenicity, the TRH is believed to act similarly to the TDH, based on genetic sequence similarity (2).…”

Prevalence of Biofilm Formation and Wide Distribution of Virulence Associated Genes among Vibrio spp. Strains Isolated from the Monastir Lagoon, Tunisia

“…against a variety of cell lines (Hiyoshi et al, 2010;Mechri et al, 2013b). Our investigation showed that V. alginolyticus isolates exhibi ted the most important cytotoxic activity against Vero and HeLa cell lines.…”

The First Report of <i>Vibrio parahaemolyticus</i> Strain O10:K60 in Japan, a New Combination of O and K Serotypes Isolated from a Patient with Gastroenteritis

“…These genes are widely considered the predominant indicators of pathogenicity in V. parahaemolyticus. In addition, the type III secretion system (T3SS) has been investigated as a potential indicator of virulence (15)(16)(17)(18). Most clinical strains contain two nonredundant T3SSs, T3SS1, and T3SS2 (19,20).…”