Purification and characterization of type II heat-labile enterotoxin of Escherichia coli

Type II heat-labile enterotoxin of Escherichia coli activates adenylate cyclase in human fibroblasts by ADP ribosylation

Type II heat-labile enterotoxin (LT-II) from Escherichia coli causes characteristic morphological changes and accumulation of cyclic AMP in Y-1 adrenal cells, but it is not neutralized by antisera against choleragen (CT) or the classical type I heat-labile enterotoxin (LT-1) from E. coli. The action of purified LT-II on CT- and LT-I-responsive human fibroblasts was investigated and compared with that of CT. Fibroblasts incubated with LT-II or CT had an increased cyclic AMP content as well as a fourfold elevation of membrane adenylate cyclase activity. In membranes, activation of cyclase by toxin was enhanced by NAD, GTP, and dithiothreitol. The effect of LT-II on intact fibroblasts or membranes was increased by trypsin treatment of toxin. Since activation of adenylate cyclase by LT-II was stimulated by NAD, the ability of LT-II to catalyze the [32P]ADP-ribosylation of membrane proteins in the presence of [32P]NAD from control and LT-II- and CT-treated fibroblasts was investigated. Similar proteins were [32P]ADP-ribosylated in membranes exposed to LT-II or CT; LT-II- and CT-specific labeling was significantly decreased in membranes prepared from cells preincubated with either LT-II or CT. These studies are consistent with the hypothesis that LT-II, similar to CT and LT-I, increases cyclic AMP by activating adenylate cyclase through the GTP-dependent ADP-ribosylation of specific membrane proteins.

Enzyme-linked synthetic oligonucleotide probes: non-radioactive detection of enterotoxigenic Escherichia coli in faecal specimens

Synthetic oligonucleotides, complementary to unique sequences in the heat stable enterotoxin gene of Escherichia coli specific for humans, were prepared with a 30-atom spacer arm and a 3' terminal sulfhydryl group which was coupled to bromoacetyl-derivatized alkaline phosphatase. The resulting direct enzyme-linked oligonucleotide probes, containing one enzyme molecule per oligonucleotide, successfully diagnosed enterotoxigenic Escherichia coli in clinical specimens by using a modified colony hybridization method and a colorimetric assay. The procedure is rapid, simple and reliable with a sensitivity equivalent to that using 5'-terminally labelled [32p]-oligonucleotide probes. The results indicate that the enzyme-labelled oligonucleotide probes should be applicable to the routine diagnosis of enterotoxigenic Escherichia coli and possess the potential for the detection of other microbial pathogens.

Production of type II heat-labile enterotoxin by Escherichia coli isolated from food and human feces

Escherichia coli strains isolated in Sao Paulo, Brazil, from feces of patients with diarrhea and from food samples produced toxin(s) that was shown to be related both immunologically and genetically to the recently characterized type II heat-labile enterotoxin of E. coli. The new isolates of type II heat-labile enterotoxin-producing E. coli belonged to five different serotypes and did not represent a single clone.

Variation in chemical properties and antigenic determinants among type II heat-labile enterotoxins of Escherichia coli

Type II heat-labile enterotoxin (LT-II) from Escherichia coli 41 was purified and compared with prototype LT-II encoded by genes from E. coli SA53. Both toxins were oligomeric proteins consisting of polypeptides A (Mr, 28,000) and B (Mr, 11,800). The A polypeptides were cleaved by trypsin into fragments A1 (Mr, 21,000) and A2 (Mr, about 7,000). These two toxins were shown to belong to two different subclasses of LT-II. We propose to designate the prototype toxin LT-IIa and the new variant LT-IIb. The pI of LT-IIb was between 5.2 and 5.6, significantly lower than the pI of 6.8 for LT-IIa, and the behavior of LT-IIb during purification differed significantly from that of LT-IIa. The toxic dose of unnicked LT-IIb in the Y1 adrenal-cell assay was 94 pg, but trypsin-treated, nicked LT-IIb was toxic at about 3 pg. In contrast, the toxic dose of LT-IIa was previously shown to be 0.5 to 1 pg for several preparations that varied from unnicked to partially nicked, and treatment with trypsin was not required for full toxicity. The titer of LT-II antiserum in neutralization tests was 100-fold greater against LT-IIa than against LT-IIb. In immunodiffusion tests, LT-IIa and LT-IIb gave a reaction of partial identity. In a radioimmunobinding assay, the titer of LT-IIa antiserum against homologous LT-IIa was approximately 10-fold greater than against LT-IIb. The cholera-E. coli family of heat-labile enterotoxins has been divided into serogroup I, which includes cholera toxin and the antigenic variants of E. coli heat-labile toxin designated LTh-I and LTp-I, and serogroup II, which includes LT-IIa and LT-IIb. The type I and type II toxins do not cross-react in neutralization or immunodiffusion tests. By using very sensitive radioimmunobinding assays, it was possible to demonstrate common antigenic determinants between the type I and type II toxins. However, the titers of antibodies in hyperimmune sera that recognized these common determinants were very low.