Partial purification and properties of Enterobacter cloacae heat-stable enterotoxin

Cell free preparations of the whole-cell lysate and ultrafiltration (UF) fractions of broth cultures of a strain of Enterobacter cloacae, isolated from a Puerto Rican with tropical sprue, were assayed for their ability to induce in vivo net water secretion in the rat jejunum. The whole-cell lysate and UM-10 retentate of broth cultures were inactive. The UM-2 retentate and filtrate were active at a concentration of 100 mug/ml or more; the toxigenic activity was entirely retained, and increased to 1 mug/ml, by a UM-05 membrane; washing this retentate yielded a fraction with an activity of 10 ng/ml. Stationary aerobic culture conditions yielded the most active UF fractions when ammonium sulfate was used as the precipitating agent, whereas anaerobic culture conditions produced the most active fractions in broth cultures precipitated by acetone. Passage of the active acetone-precipitated UF fractions through a Sephadex G-25 column yielded eluate pools with enhanced toxigenic activity in, or adjacent to, the void volume, but maximum activity of the ammonium sulfate-precipitated UM-05 retentate eluated at a Kav of 0.38 to 0.52. Neither of the most active gel filtration elution fractions of the UM-05 retentates contained detectable carbohydrate, suggesting that the toxin is not associated with endotoxin. Toxigenic activity was unaltered by exposure to a temperature of 100C for 30 min, lowering the pH to 1, or incubation with either Pronase or trypsin. These observations indicate that the strain of E. cloacae under study elaborates a heat-stable enterotoxin htat has approximately the same molecular weight and shares many of the characteristics of the heat-stable enterotoxin produced by some strains of Escherichia coli and Klebsiella pneumoniae.