ABSTRACT
Aeromonas hydrophila secretes several extracellular proteins including enterotoxin, hemolysin and aerolysin that are associated with the bacterial virulence. Previous studies have shown that two hemolytic toxins, hemolysin A and aerolysin A contribute to the virulence of Aeromonas hydrophila. In the current study, a total of 50 strains of Aeromonas hydrophila, including 28 [56%] strains isolated from diarrheal cases and 22 [44%] strains isolated from healthy asymptomatic controls, were used. These strains were tested for cytochrome oxidase activity based on Kovac's method and confirmed as A. hydrophila with API 20E multi-test systems. To determine hemolysin, cytotoxin and enterotoxin activities, horse blood agar, Vero cells and the suckling mouse model were used, respectively. The presence of two hemolytic toxin genes: hlyA and aerA was determined by PCR assay. About 89% of diarrheal strains tested were positive for hemolysins, 68% for cytotoxin and 89% for enterotoxin activity. These figures for healthy asymptomatic isolates were 72%, 23% and 14%, respectively. A significant association was found between cytotoxin and enterotoxin activity in diarrheal disease, whereas such association was not found in case of hemolysin. Almost 93% of diarrheal isolates and 73% of healthy person strains were PCR positive for hly A gene. The corresponding figures for aerA gene were 86% and 45.5% respectively. The aerA + hlyA + genotype and in some cases aerA + genotype could be considered as reasonable predictors of human diarrheal disease. However, the role of other unknown hemolytic and cytolytic factors cannot be discounted