Heat-labile enterotoxins of Escherichia coli

Heat-labile high molecular weight enterotoxin from porcine and human strains of Escherichia coli has been purified in several laboratories in recent years. Data reported concerning enterotoxin purified from cell lysates, cell envelope-associated toxin and toxin in the culture fluids are different and do not seem reproducible from one laboratory to another, due to at least two facts: (1) aggregation of enterotoxin with high molecular weight material such as endotoxin (ii) activation of protoxin by bacterial protease. Conventional methods such as ion exchange and molecular sieve chromatography did not yield toxin of high purity while preparative isotachophoresis and isoelectric focusing in density gradiants and granulated gels were used with increased recovery of purified enterotoxin. The toxin was found to be heterogeneous concerning charge properties and focused in pH ranges 4·8–5·5 and 7·2–7·9. Sepharose 2B chromatography resolved two enterotoxins with different specific activities in the intestinal loop test and the adrenal cell test. The relationship of these preparations of partially purified toxin to enterotoxins with different relative activities in the rabbit intestinal loop and skin test, different cell tests and the adenylate cyclase test is discussed in relation to the subunit composition of cholera toxin which has a similar mode of action, but different chemical composition despite immunological cross-reaction between the cholera and E. coli enterotoxins.