Tetrathionate Broth Base 500 g

Tetrathionate is formed by the iodine reaction with sodium thiosulfate. This combination (sodium thiosulfate and tetrathionate) suppresses commensal intestinal organisms. The organisms which have the enzyme tetrathionate reductase, such as Salmonella, proliferate in this medium. However, Proteus also contains this enzyme, but its growth can be minimized by adding 4 mg/L of novobiocin before adding the iodine solution. Peptone provides nitrogen, vitamins, minerals and amino acids essential for growth. Bile salts are inhibitors of other Gram-positive organisms. Calcium carbonate neutralizes and absorbs toxic metabolites.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Suspend 46 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. AVOID OVERHEATING. DO NOT AUTOCLAVE. Cool to 45-50 °C and aseptically add 20 mL per liter of an iodine solution to the medium on the same day of its use. Homogenize gently and dispense into sterile containers. Prepare the iodine-iodide solution by dissolving 6 g of iodine crystals and 5 g of potassium iodide in 20 mL of distilled water. Dispense 10 mL into tubes, continually swirling the flask to maintain homogeneity.

Instructions for use

1. Inoculate each 10 mL tube with 1-2 g of the sample (wastewater, etc.) and incubate at 35 ± 2 °C for 18-24 hours.
2. Growth is indicated by turbidity in the medium.
3. After incubation, subculture onto selective plated media for Salmonella, such as MacConkey Agar (LC-1052), Bismuth Sulfite Agar (LC-1011), Desoxycholate Agar (LC-1020), Brilliant Green Agar (LC-1078), XLD Agar (LC-1274) or Hektoen Enteric Agar (LC-1030), and incubate at 35 ± 2 °C for 18-24 hours.

• American Public Health Association Recommended Methods for the Microbiological Examination of Foods, APHA, Inc. New York, 1958.
• American Public Health Association Standard Methods for the Examination of Dairy products. Eleventh Edition, APHA, Inc. New York, 1960.
• Kauffmann 1930. Zentralbl. Bacteriol. Parasitenkd. Infektionskr. Hyg. Abt. Orig. 113-148.
• United States Pharmacopeial Convention, Inc. 2001. The United States pharmacopeia 25/The national formulary 20 - 2002. United States Pharmacopeial Convention, Inc., Rockville, Md.