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Clostridium difficile causes pseudomembranous colitis in humans and a similar ileocecitis in hamsters. This organism can colonize the intestines after antibiotic therapy disrupts the normal intestinal microflora. Once established in the intestines, the organism causes disease by producing two toxins, designated toxin A and toxin B. Only toxin A is active on intestinal epithelium, thus toxin A is the cause of the initial tissue damage in the intestines. In order for a toxin to affect a cell, it must first bind to the cell. Toxin A has been shown to bind to Galα1- 3Galβ 1-4GIcNAc on the intestinal epithelium of hamsters. I provide evidence that toxin A can use this trisaccharide as a functional receptor on cell lines, and that the expression of the carbohydrate receptor increases the sensitivity of the cells to toxin A. Furthermore, the intestinal epithelium of infant hamsters bound less toxin A at 37C than did the adult tissue, and infants are less sensitive to the disease caused by C. difficile than are adults. This provides further evidence that the activity of toxin A is increased by the binding of the toxin to Galα1-3Galβ1- 4GlcNAc. Even though Galα1-3Galβ 1-4GlcNAc was a receptor for toxin A on animal cells, it probably is not a receptor for toxin A in humans, because people do not normally express this carbohydrate. Instead, I found that toxin A bound to the carbohydrate antigens designated I, X, and Y, which are present on the intestinal epithelium of humans. These carbohydrates could be receptors for toxin A. The possible significance of these receptors is discussed. Ph. D.

Bradyrhizobium japonicum USDA 143 grew chemoorganotrophically when supplied with exogenous nitrous oxide as the terminal electron acceptor, or as the alternate terminal electron acceptor to nitrate under anoxic conditions. Cell growth and dissimilatory N₂O reduction were significantly inhibited by acetylene when either N₂O or N₂O plus nitrate served as terminal electron acceptor(s). Reduction of nitrous oxide accounted for 20% of the energy for cell growth in cultures supplied with nitrate as the terminal electron acceptor. Nitrous oxide was produced stoichiometrically in cultures supplied with nitrate and acetylene and growth was proportionately reduced compared to cultures supplied with an equal amount of nitrate. Exogenous nitrous oxide delayed the reduction of nitrate in cultures supplied with both electron acceptors. The final cell yield and/or growth rate of the cells were reduced when N₂O was ≥ 15% of the culture flask headspace. Direct amperometric monitoring of nitrous oxide respiration indicated a specific activity of 0.082 ± 0.004 µmoles N₂O/min/mg cell-protein. The respiration was inhibited by azide. A Clark-type electrode with a platinum cathode, and the instrumentation for monitoring hydrogen uptake amperometrically were used to monitor the reduction of N₂O during anaerobic respiration. Master of Science

A method is provided for detecting the presence of C. difficile toxin A. Stool or other appropriate specimen is contacted with a reagent containing the human X, Y or I-antigens, each of which is a specific receptor for toxin A. The reagent may be intact cells, cell membranes, membrane fractions containing any of these antigens, glycoconjugates, as well as the purified oligosaccharide antigen per se. Binding of toxin A is determined by conventional assay techniques. The method may also be used to isolate and purify toxin A. Conversely, immobilized toxin A may be used to detect, isolate, or purify biological materials of interest expressing the X, Y or I antigens.