Techniques for the isolation of salmonellae and the quality control of enrichment and selective media

The basic techniques used for the isolation of salmonellae are discussed. These methods are exceptional in that they involve the isolation of very low numbers of salmonellae in the presence of very high numbers of competing microbes. There is a multiplicity of variations in terms of media, incubation temperatures and times, and even methods of surface plating are considered important. Except for recommendations for quality assessment trials, little has been done in checking the productivity of media for isolating salmonellae. If tests are to be devised, a small selection of the many available pre-enrichment, enrichment and selective media will have to be chosen and a testing protocol devised which will take account of the effect of the food sample and of sublethally damaged salmonellae on the pre-enrichment medium, as well as the competing flora in all media.