Diagnostic Semi Solid Salmonella Agar (Diassalm)

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Diassalm, as developed by Van Netten et al (1991), is a semi-solid differential medium for the isolation of Salmonella spp. from food and water. It is an improved modification of MSRV (De Smedt and Bolderdijk 1988) and SR (Perales and Audicana 1989) with regard to the composition of the basal medium, selective system and the introduction of a differential system. The original basal medium was a commercially available sulphide mobility-indole medium (SIM BBL) (Blazevic 1968). Lab M have substituted their raw materials into Blazevic’s formula to create a richer base for Diassalm. Selectivity is achieved by the use of malachite green oxalate, magnesium chloride and novobiocin. The diagnostic properties of Diassalm are based on the use of two indicator systems; saccharose combined with bromocresol purple; and ferro-iron in combination with thiosulphate. The efficiency of Diassalm is due to the ability of salmonellae to move through the highly selective mobility medium in a Petri dish, whilst the double diagnostic system allows visualisation of motile and non-motile suspected salmonellae due to blacking zones against the turquoise background. Diassalm can be seeded after preenrichment or after 8hr enrichment in selective broth (De Smedt and Bolderdijk 1987).