PRODUCTION OF ESCHERICHIA-COLI STB ENTEROTOXIN IS SUBJECT TO CATABOLITE REPRESSION

Enterotoxigenic Escherichia coli are known to secrete several types of toxins including STb, a heat-stable enterotoxin. STb enterotoxin prod uction was studied in wild-type E. coli strains. Using a quantitative STb-specific inhibition ELISA, the amount of toxin present in the cult ure supernatant fractions of various E. coli strains was determined. V ariation in the production of STb toxin was observed for the wild-type strains. For E. coli strain 82-4247 grown in trypticase soy broth, th e toxin was produced after 4 h of growth and was maximal after about 5 7 h of growth. The amount of toxin in the culture supernatant fraction increased concomitantly with bacterial growth. Using the rat loop ass ay, the biological activity of STb was retained even after the logarit hmic phase of growth when STb production levelled off (i.e. from 24 to 74 h). STb production by E. coli strain 82-4247 varied with the cultu re medium used. In particular, addition of 1.0% (w/v) compared to 0.1% glucose to Davis minimal medium decreased STb production, whereas add ition of 1.0% (w/v) glycerol did not affect STb production. Addition o f exogenous cAMP reversed the repressive effect of glucose. Using muta nt strains, STb production was shown to be subject to catabolite repre ssion.