Production of Shiga-Like Toxin by Escherichia coli Escherichia coli is one of several agents that cause intestinal disease in humans and animals. Four classes of E. coli have been recognized [1], Enterotoxigenic E. coli (ETEC) strains produce a heat-labile (LT) enterotoxin and/or a heat-stable (ST) enterotoxin. Enteroinvasive E. coli (EIEC) strains, like shigellae, penetrate and multiply within epithelial cells. Enteropathogenic E. coli (EPEC) strains belong to certain serogroups that have been incriminated as pathogens by epidemiological studies. Some EPEC strains have been shown to adhere to cells of the intestinal mucosa and to produce pathognomonic lesions at the site of attachment. Enterohemorrhagic E. coli (EHEC) strains cause a distinct clinical syndrome (hemorrhagic colitis), and serotype 0157:H7 has been associated with this illness. Neither EPEC nor EHEC strains produce classic enterotoxins, nor are they enteroinvasive. Some strains of E. coli produce a cell-associated cytotoxin that is neutralized by antibodies against purified Shiga toxin from Shigella dysenteriae type 1 [2-4]. The cytotoxins purified from one EPEC strain 026:H11 (H30) and from one EHEC strain 0157:H7 (933) have biologic activities (cytotoxicity for HeLa and Vero cells, lethality for mice, and enterotoxicity for ligated ileal segments from rabbits) and subunit structures similar to those of Shiga toxin [5, 6]. The purpose of this study was to determine the frequency and levels of cytotoxin production for a wide variety of E. coli strains. Culture supernatants and sonic lysates of 418 strains isolated from humans, animals, ajid food were examined for cytotoxic effects on HeLa cells and to see whether cytotoxicity could be neutralized by antibodies to Shiga toxin. Materials and Methods Bacterial strains. E. coli strains examined for production of Shiga-like toxin were obtained mainly from the Centers for Disease Control, Atlanta, Georgia. The 418 strains were isolated over a period of 30 years from the following: humans with diarrhea, hemorrhagic colitis, hemolytic uremic syndrome, or no clinical manifestation of disease; calves with diarrhea; piglets with edema dis

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Previous studies have shown that the pattern and degree of 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine ([125I]TID) photoincorporation into the nicotinic acetylcholine receptor (nAChR) can be used as a sensitive measure of nAChR conformation. Upon desensitization by prolonged exposure to agonists, certain drugs and detergents, or reconstitution into desensitizing lipids, the levels of [125I]TID incorporation into the subunits of the nAChR are dramatically reduced. In this study, we characterized the effects of the snake venom proteins alpha-bungarotoxin and alpha-cobrotoxin, as well as the smaller antagonists tubocurarine and gallamine, on [125I]TID incorporation into the subunits of both partially-purified nAChR in native lipids, or affinity-purified nAChR reconstituted into different combinations of lipids. Unlike all other compounds previously tested, alpha-bungarotoxin and alpha-cobrotoxin reproducibly increased the level of [125I]TID incorporation into all four subunits of nAChR reconstituted into dioleoylphosphatidylcholine, dioleoylphosphatidic acid and cholesterol. Gallamine had little or no effect on [125I]TID incorporation at any concentration tested (0.1 microM-5 mM). Tubocurarine had no effect on [125I]TID incorporation at low concentrations, but at higher concentrations reduced the level of [125I]TID labeling. The snake venom proteins may shift the population of nAChR, which exists as a mixture of resting state and desensitized conformations, entirely to the resting state. However, the binding of the snake venom toxins does not appear sufficient to induce the resting state conformation in nAChR which have been desensitized by other means, such as solubilization in desensitizing detergents or reconstitution in densitizing lipids.

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Postcontraction depression of Hoffmann-reflex (H-reflex) amplitudes was examined to study the rationale underlying proprioceptive neuromuscular facilitation relaxation techniques. The time course of H-reflex amplitude depression was used to assess postcontraction changes in motoneuron reflex excitability. Sixteen healthy female subjects performed voluntary isometric plantar-flexion contractions (65%-75% of maximal voluntary contraction) in a prone position. H-reflex stimulation began at a postcontraction delay of 0.05, 0.1, 0.5, 1, or 5 seconds and continued every 10 seconds for 1 minute. Reflexes were depressed (mean = 67% decrease) by 0.05 second postcontraction, reached maximal depression (mean = 83.3% decrease) from 0.1 to 1 second postcontraction, recovered to 70% of control amplitudes (mean = 30% decrease) by 5 seconds postcontraction, and reached 90% control amplitudes (mean = 10% decrease) by 10.05 seconds postcontraction. The results indicate that proprioceptive neuromuscular facilitation techniques (eg, hold-relax) purported to produce a phase of relaxation following voluntary contraction do appear to produce a strong, but brief, neuromuscular inhibition that may be clinically useful for applying stretch.