Tetrathionate Broth Base was first formulated by Mueller (1) who showed that this medium favours the unrestricted growth of enteric pathogens by selectively inhibiting the coliforms. Muellers medium was subsequently modified by Kauffman (2) and Knox (3) in which they obtained more number of isolates. Tetrathionate Broth Base, Hajna is the modification formulated by Hajna and Damon (4). This medium is recommended by APHA (5) for the selective enrichment of Salmonellae from foodstuffs. Peptone special and yeast extract are the sources of carbon, nitrogen, vitamins and minerals. The selectivity depends on the ability of thiosulphate and tetrathionate (formed by the addition of iodine-iodide) to suppress commensal coliform organisms (6, 7). Sodium deoxycholate and brilliant green inhibit gram-positive organisms. Dextrose and Mannitol are the carbohydrates sources. Calcium carbonate neutralizes the acidic tetrathionate decomposition products. Sodium chloride maintains the osmotic balance of the medium. After enrichment of the sample, streak on the plates of Brilliant Green Agar (M016), MacConkey Agar (M081), Bismuth Sulphite Agar (M027) for further confirmation.
Directions: Suspend 91.51 grams in 1000 ml distilled water. Heat to boiling to dissolve the medium completely or place in flowing steam for 30 minutes. DO NOT AUTOCLAVE. Cool to 45°C. Mix and add 40 ml of Iodine solution (8 g potassium iodide and 5 g iodine per 40 ml). Mix and dispense 10 ml amounts in tubes. Do not heat after addition of iodine.
Note: Due to the presence of calcium carbonate, the prepared medium forms opalescent solution with a white precipitate.