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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Aims: To develop a readily applicable polymerase chain reaction (PCR) based technique which would permit the identification of Mycobacterium tuberculosis complex isolates from Bactec phials at an earlier stage than currently available methods. Methods: Mycobacterial cells cultured in Bactec 12B medium were harvested by centrifugation. The cells were lysed by heating in distilled water. Oligonucleotide primers based on the sequence ofthe gene coding for the immunogenic protein MPB64 were then used to amplify a 240 base pair fragment of DNA directly from the crude cell lysate. The PCR product was visualised under ultraviolet light following electrophoresis of an aliquot in an agarose gel containing ethidium bromide.

Strains of gonococci to act as indicators were selected initially by trial and error, cross streaking each member of a group of isolates against all the others and selecting suitable ones for further testing. In order to prevent the degradation of the selected strains by repeated subculture, they were suspended in 100% horse serum broth and frozen in liquid nitrogen. At the same time a number of samples of each strain were freeze dried. When strains from liquid nitrogen were required for use they were thawed rapidly and grown on chocolate agar. The growth was scraped off and a suspension made in a small volume in nutrient broth. The indicator strains were then streaked across the original inoculum at right angles, using a platinum loop of 3 mm in diameter. The plates were then incubated in 10% CO2 at 37°C for 18 hours and the results of inhibition of indicator strains were recorded as either complete inhibition, thinning of growth only, or no inhibition.

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