We have constructed a general-use vector for the cloning and stable expression of foreign genes in the chromosome of attenuated Salmonella typhimurium. Using this chromosomal expression vector (CEV), we expressed the circumsporozoite (CS) gene of the mouse malaria Plasmodium yoelii in an aroA S. typhimurium strain. Mice immunized with CS-expressing Salmonella recombinants mount a CS-specific cytotoxic T-lymphocyte (CTL) response. This is the first demonstration that attenuated Salmonella can elicit a specific CTL response to a foreign protein in mice. The ability to easily and stably express foreign genes from the Salmonella chromosome and the generation of specific CTL greatly expands the potential of Salmonella as an antigen-delivery system.

The whole-body retention of mercury after exposure of BALB/c mice to methylmercury was measured in animals fed fibre-free, 5% pectin, 5% cellulose or 5, 15 or 30% wheat bran diets. The rate of elimination of mercury was dependent on the diet fed, with dietary bran increasing the rate of elimination. The incorporation of 15 or 30% bran in the diet of the mice decreased the total mercury concentration in the brain, blood and small intestine, although the effects were significant only in those animals on 30% bran diet. The fibres had little effect on mercury levels in other tissues. The proportion of mercury found in the mercuric form was significantly greater in liver, kidneys and gut of mice fed bran. The results suggest that dietary bran may reduce the levels of mercury in the brain after methylmercury exposure and may therefore reduce the neurotoxic effects of the organomercurial. We suggest that wheat bran exerts its effects on mercury retention and brain level via a modification of the metabolic activity of the gut microflora.

(Cowan, 1969), tonsils (Hellgren, 1971; Iqbal, 1971), and skin (Barr and Danielsson, 1971). The standard method used to identify neisseria is the fermentation reactions when tested against glucose, maltose, and sucrose. A disadvantage of the serum agar slopes of these sugars is that many laboratories find difficulty in interpreting the results owing to the occurrence of a non-specific change in the indicator which sometimes develops and often makes the interpretation of the maltose results impossible and, moreover, leads to a complete lack of confidence in the test. The identification of a suspected pathogen is always desirable but this will not be achieved when gonococci are isolated from sites where other neisseria are likely to be found, unless the fermentation tests employed are absolutely reliable.

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