Characterization and Distribution of Virulence Factors in Aeromonas hydrophila Strains Isolated from Fecal Samples of Diarrheal and Asymptomatic Healthy Persons, in Ilam, Iran

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 hlyA 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