Mueller Kauffman Tetrathionate Novobiocin Broth Base (MKTTn broth base)
This is a selective enrichment broth for the isolation of Salmonella spp. primarily from food and food product samples and conforms to the requirements ISO 6579:2002. It can however be used in other areas including clinical and environmental specimens. Salmonella spp. reduce tetrathionate and will proliferate in the medium whilst most other enteric organisms are inhibited. Unlike the older traditional tetrathionate broth the addition of novobiocin (40 mg/l) improves the inhibition of Proteus spp.
Immediately prior to use it is necessary to add 20 ml/l of 2% iodine/iodide solution Once the iodine/iodide solution has been added the medium should be used immediately and cannot be stored for future use.
NB: As this is an opaque medium, the turbidity of the broth alone cannot be used as an indication of growth.
Principles and uses
Muller-Kauffmann Broth Base with Brilliant Green and Novobiocin (MKTTN) is recommended by the ISO 6579 and ISO 19250 norms to be used as a selective enrichment broth for the detection of Salmonella spp in all food types, including milk and dairy products, molluscan shellfish and other fish products, and in water samples and environmental swabs.
Beef extract and casein peptone provide nitrogen, vitamins, minerals and amino acids essential for growth. Calcium carbonate is a neutralizer which absorbs toxic metabolites. Bile salts, brilliant green and novobiocin inhibit organisms other than Salmonella. Selectivity is also obtained by both sodium thiosulfate and tetrathionate, suppressing coliforms. Tetrathionate is formed in the medium with the addition of the iodine and potassium iodide solution.
Organisms containing the enzyme tetrathionate reductase will thrive in this medium. Sodium chloride supplies essential electrolytes for transport and osmotic balance.
Preparation
Suspend 89,53 grams of the medium in one litre 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 45-50ºC. Aseptically Add 20 ml of an iodine and potassium iodide
solution (20 g of iodine and 25 g of potassium iodide in 100 ml of sterile distilled water). Homogenize gently and dispense into sterile containers.
