IRON SULPHITE AGAR

Iron Sulphite Agar is a modification of Cameron Sulphite Agar developed by the National Canners Association of America. It was shown by Beerens that 0.1% sulphite concentration in the original formula was inhibitory to some strains of Clostridium sporogenes. This observation was later confirmed by Mossel et al, who consequently showed that 0.05% sulphite concentration was not inhibitory to the organisms. Most clostridia have sulfite reductase in their cytoplasm but they are unable to expel them to the exterior. So when H2S is produced from sulfite, the colony becomes dark due to the formation of precipitates of iron sulfide from citrate.
For the detection of organisms causing sulphide spoilage, two methods can be followed:
Deep-Shake Culture Method: Dispense the medium in 10 ml amounts in tubes. Inoculate the sample when the medium is at about 50?C. Allow to set and incubate at 55?C for 24-48 hours. Typical thermophilic species -Desulfotomaculum nigrificans, produces distinct black spherical colonies in the depth of the medium.

for detection of thermophillic anaerobic organisms causing sulphide spoilage in foods