Purification and properties of Klebsiella pneumoniae heat-stable enterotoxin.

The enterotoxic material in cell-free growth preparations of Klebsiella pneumoniae serotype 5 was purified by sequential ultrafiltration and gel filtration (GF) procedures and the fractions were assayed for enterotoxic activity by determining their ability to induce in vivo net water secretion in the rat jejunum. Whole-cell lysates were inactive. Anaerobic broth culture conditions yielded a 10-fold increase in toxin production over aerobic conditions. Enterotoxic activity was absent in the UM-10 retentate of the broth filtrate but present in both the retentate and filtrate of the UM-2 membrane. GF of the two UM-2 ultrafiltration fractions through a Sephadex G-25 column yielded an active eluate, whose potency was increased by 10- or 200-fold, in or adjacent to the void volume. When subsequently passed through a G-50 column, these pools eluted at a Kav of between 0.4 and 0.6 and were further increased in potency by two- or fivefold. A second equally potent fraction was also recovered in the void volume of the G-50 eluate of the UM-2 filtrate; this may represent a polymer. Progressive purification by GF was associated with an increased protein and decreased carbohydrate content of the most active fractions. The most active G-50 eluate of the UM-2 retentate had a minimal effective enterotoxic dose of 5 mug/ml and that of the filtrate was less than 0.1 mug/ml. Heating the active GF eluates to 100 C for 30 min did not abolish enterotoxic activity and lowering the pH to 1 or incubation with either Pronase or trypsin had no effect on activity. These observations indicate that K. pneumoniae heat-stable enterotoxin is probably a single toxin with an apparent molecular weight in the range of 5,000. The elution characteristics during GF as well as the chemical composition of the most purified enterotoxin fractions indicate that the toxin is not associated with endotoxin.