Pathogenicity ofAeromonas hydrophila in red leg disease in frogs

Endotoxin and hemolysin fromAeromonas hydrophila A₃ were studied to understand the pathogenicity of the organism. Neither the endotoxin nor the hemolysin alone produced typical red leg disease symptoms or death in frogs, even at a very high dosage of 8,000 μg; however, endotoxin and hemolysin together did. Further, histamine-stressed frogs died from hemolysin but not endotoxin. Hemolytic activity of hemolysin increased in cells that were preincubated with endotoxin. Results point to the conclusion that red leg disease in frogs represents a complex interaction between endotoxin and hemolysin and that stress-producing factors other than the endotoxin might trigger disease production.