Studies on the use of gamma radiation for the elimination of salmonellae from whole egg, frozen horse-meat, desiccated coconut and bone meal show the extent to which the nature of the medium influences the resistance of these organisms to gamma radiation. There is also a variation in radiation resistance between different serotypes; S. typhi-murium was consistently the most resistant of those examined.
Based on experiments with artificially inoculated or naturally contaminated products, and also on dose/survival curve data, the dose requirement for the elimination of salmonellae from frozen whole egg is estimated at 0·5 Mrad., which gives a 107 reduction in numbers of S. typhi-murium; for frozen horsemeat 0·65 Mrad., giving a 105 reduction; and for bone meal between 0·5 and 0·75 Mrad., giving between 105 and 108 reduction. A dose of 0·45 Mrad. appears effective for desiccated coconut, with a reduction of 103, but such a radiation dose affects the quality of this product.
We are grateful to Dr E. S. Anderson of the Enteric Reference Laboratory for phage typing and for the provision of a strain of S. typhi-murium for experi ments. Also we thank Dr Joan Taylor of the Salmonella Reference Laboratory for the serological typing of salmonellae, and Miss M. E. Smith and other colleagues of the Food Hygiene Laboratory who carried out the routine bacteriological examination.
We wish to thank Mr N. C. Roberts of J. Rannoch Ltd. for his co-operation in the large-scale frozen egg experiment, and also Mrs G. M. Ison of S. Wallace Ltd. in respect of the experiment on frozen horse-meat.