Thermophillic bacteria are usually species of Bacillus which enter milk from various sources on the farm or from poorly cleaned equipments in the processing plant. These bacteria rapidly increase in numbers when present in milk or dairy products that are held at high temperature for long periods. Sour spoilage of food products without formation of gas is called as flat-sour spoilage. M-Dextrose Tryptone Broth is a modification of Dextrose Tryptone Agar. This is a non-selective medium, useful for the cultivation of a variety of microorganisms. Olson et al (1) used M-Dextrose Tryptone Broth for determining total counts on samples of milk passed through welded milk lines.
Casein enzymic hydrolysate supplies essential growth nutrients. Dextrose is the fermentable carbohydrate and bromocresol purple acts as the pH indicator. Color change of the medium from purple to yellow is due to acid production from dextrose.
Test samples are filtered through membranes and then placed on membranes saturated with M-Dextrose Tryptone Broth and incubated at 55°C in sealed Petri plates for the detection and enumeration of thermophilic flat-sour sporulating organisms (2).
Storage and Shelf-life:
Store below 30°C in tightly closed container and the prepared medium at 2-8°C. Use before expiry date on the label.
References:
1. Olson, Brown and Mickle, 1960, J. Milk and Food Tech., 23:86.
2. MacFaddin J. F., 1985, Media for Isolation-Cultivation-Identification-Maintenance of Medical Bacteria, Vol. I, Williams and Wilkins, Baltimore.