Iron Sulphite Agar Modified is recommended for enumerating sulphite-reducing bacteria, including clostridia, growing under anaerobic conditions, with composition and performance aligned to ISO 15213-1 (2023) and ISO 11133. Peptone, soya digest and yeast extract nourish the organisms while sulphite and an iron source act as the indicator system. Reduction of sulphite produces iron sulphide and characteristic black colonies that are easily counted. Widely used in food and water microbiology. Dehydrated powder, store in a cool dry place. Packaged as 500 g.