A low molecular weight enterotoxic hemolysin from clinical Enterobacter cloacae

Seven of 50 Enterobacter cloacae strains from clinical isolates produced small turbid zones of hemolysis in horse and sheep blood agar plates, and the culture supernatants were also positive for hemolytic activity. The hemolysin was partially purified from the culture supernatant of E. cloacae by ultrafiltration (PM-10 membrane) and extraction with acetone. Semipurified hemolysin was stable to heating (100 degrees C, 30 min) and was soluble in organic solvents (acetone, ethanol, and methanol). The toxin showed no loss of biological activity after treatment with trypsin and was stable to acid treatment at pH 2.0 but not at a pH greater than 7.0. In the rat intestinal loop assay, the hemolysin caused hemorrhagic fluid accumulation and severe histological alterations. These findings indicate that this hemolysin may be a putative virulence factor in E. cloacae infections.