M-Dextrose Tryptone Broth

M-Dextrose Tryptone Broth

M-Dextrose Tryptone Broth is used for detection and cultivation of thermophilic flat sour microorganisms from food preparations using membrane filter technique.

Composition**

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 30.04 grams in 1000 ml distilled water. Heat if necessary to dissolve the medium completely. Dispense as desired and sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.

Principle And Interpretation

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. Colour 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).

Quality Control

Appearance Cream to light green homogeneous free flowing powder

Colour and Clarity of prepared medium Purple coloured clear solution without any precipitate

Reaction Reaction of 3.0% w/v aqueous solution at 25°C. pH : 6.7±0.2

pH 6.50-6.90

Cultural Response

M1104: Cultural characteristics observed after an incubation at 55°C for 36-48 hours in humid atmosphere.

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.

Reference

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.