It has now been established that transmissible spongiform encephalopathy (TSE) infectivity, which is highly resistant to conventional methods of deactivation, can be transmitted iatrogenically by contaminated stainless steel. It is important that new methods are evaluated for effective removal of protein residues from surgical instruments. Here, radio-frequency (RF) gas-plasma treatment was investigated as a method of removing both the protein debris and TSE infectivity. Stainless-steel spheres contaminated with the 263K strain of scrapie and a variety of used surgical instruments, which had been cleaned by a hospital sterile-services department, were examined both before and after treatment by RF gas plasma, using scanning electron microscopy and energy-dispersive X-ray spectroscopic analysis. Transmission of scrapie from the contaminated spheres was examined in hamsters by the peripheral route of infection. RF gas-plasma treatment effectively removed residual organic residues on reprocessed surgical instruments and gross contamination both from orthopaedic blades and from the experimentally contaminated spheres. In vivo testing showed that RF gas-plasma treatment of scrapie-infected spheres eliminated transmission of infectivity. The infectivity of the TSE agent adsorbed on metal spheres could be removed effectively by gas-plasma cleaning with argon/oxygen mixtures. This treatment can effectively remove 'stubborn' residual contamination on surgical instruments.

Neocallimastix frontalis zoospores showed chemotaxis to a range of carbohydrates, but not to the common amino acids, purines, pyrimidines or vitamins. Four chemoreceptors were identified : the glucose receptor, sensitive to D-glucose, D-galactose, D-XylOSe, L-sorbose, D-fucose and a-deoxy-~-g~ucose; the sucrose receptor, sensitive to sucrose, D-fructose and raffinose; the mannose receptor, sensitive to u-mannose and D-glucose; and the sorbitol receptor, sensitive to D-sorbitol and D-mannitol. Growth of the vegetative stage of N . frontalis did not occur with D-xylose, L-sorbose, D-fucose, 2-deoxy-~-glucose, raffinose, u-mannose or D-sorbitol. The zoospores were attracted to carbohydrate mixtures representing the soluble carbohydrates found in different barley tissues; the highest response was with those mixtures representing carbohydrates of awn and inflorescence tissue. Chemotaxis also occurred preferentially to the awn and inflorescence tissue carbohydrate combinations rather than to carbohydrate combinations representing other tissues. Germination of the zoospores occurred in medium containing glucose in excess of I O -~ M. I N T R O D U C T l O NThe flagellated zoospores of the rumen phycomycete fungus Neocallimastix frontalis are released from sporangia borne on the vegetative stage of the organism soon after the host animal eats (Orpin, 1975). The zoospores may invade, germinate upon and grow at the expense of plant tissue present in the rumen (Orpin, 1977). Not all plant tissues are invaded by the zoospores to the same extent; a marked preference is shown for inflorescence tissue where the zoospores germinate principally at the stomata and on damaged areas. Growth of the single rhizoid results in penetration of the plant tissue through the stoma or damaged epidermis. Because of the marked substratum selection shown by the zoospores and their germination at the stomata, chemotaxis was thought likely to be operative. The chemotactic response of N . frontalis zoospores with a range of carbohydrates, amino acids, purines, pyrimidines and vitamins has now been examined. On the basis of these results, a mechanism is suggested for the preferential attraction of the zoospores to inflorescence tissues of grasses in the rumen. M E T H O D SAnimals. Sheep, Clun Forest wethers, each fitted with a permanent rumen cannula, were fed I kg hay chaff and IOO g rolled oats daily.Preparation of rumen fluid and zoospore suspensions in fresh rumen fluid. Centrifuged rumen fluid and sterile reduced rumen fluid supernatant were prepared according to Orpin (1977). Rumen fluid, used as a 8-2

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