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Material Safety Data Sheet

Organisms

Organisms this product works with:

Dehydrated Culture Media

DEXTROSE TRYPTONE BROTH

Code: CM0073

A liquid medium for the bacteriological examination of canned foods etc. Acid producing organisms such as `flat-sour’ thermophiles change the colour of the medium from purple to yellow.

Typical Formula*

gm/litre

Tryptone

10.0

Dextrose

5.0

Bromocresol purple

0.04

pH 6.9 ± 0.2

* Adjusted as required to meet performance standards

Directions
Add 15g to 1 litre of distilled water. Mix well and distribute into final containers. Sterilise by autoclaving at 121°C for 15 minutes.

Description
Dextrose Tryptone Broth is widely recommended for the aerobic cultivation and detection of many different organisms causing spoilage in canned foods and other products.

The American Public Health Association1 and Baumgartner and Hersom2 recommended this formulation for the bacteriological examination of low and medium-acid canned foods (pH 4.5 and above). Both methods include inoculation of 10ml amounts of the broth with one or two grams of the food product. For food products in this pH range, the suggested procedure is aerobic cultivation in Dextrose Tryptone Broth in parallel with anaerobic cultivation in other media; Liver Broth CM0077 is most suitable for this purpose. Duplicate sets of tubes are incubated at 35°C and at 55°C. Organisms which produce acid from dextrose, such as Bacillus stearothermophilus and other `flat-sour’ organisms, are detected by the colour change of the medium from purple to yellow.

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared broth below 25°C.

Appearance
Dehydrated medium: Pale green coloured, free-flowing powder
Prepared medium: Purple coloured solution

Quality control

Positive control:

Expected results

Bacillus stearothermophilus ATCC® 12976

Turbid growth; acid

Negative control:

 

Uninoculated medium

No change

* This organism is available as a Culti-Loop®

References
1. American Public Health Association (1976) Compendium of Methods for the Microbiological Examination of Foods. APHA Washington DC.
2. Baumgartner J. G. and Hersom A. C. (1956) `Canned Foods’ 4th ed., Churchill Ltd. London, pp. 229-230 and 247.

 
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