DEXTROSE TRYPTONE AGAR
(7340)


Intended Use


Dextrose Tryptone Agar is used for isolation of mesophilic or thermophilic
spoilage microorganisms from food.


Product Summary and
Explanation


Dextrose Tryptone Agar evolved
from research by Williams, while studying the cultivation and enumeration of
thermophilic bacteria caused by “flat-sour” spoilage of canned foods.1 In the 1930’s,
the National Canners Association specified the use of Dextrose Tryptone Agar
for isolating “flat sour” organisms from food products.2 “Flat sour”
spoilage of canned foods is caused by Bacillus coagulans (Bacillus
thermoacidurans). Bacterial growth results in a 0.3 – 0.5 drop in pH, while
ends of the can remain flat. B. coagulans is a soil microorganism, found
in canned tomato products and dairy products. Conditions favorable for organism
growth can result in spoilage of food products.3


Dextrose Tryptone Agar can be
used to isolate other food spoilage bacteria including mesophilic, aerobic
spore-formers and thermophilic “flat sour” spore-formers such as B.
stearothermophilus.3


Principles of the Procedure


Enzymatic Digest of Casein is
the carbon, nitrogen, and vitamin sources used for general growth requirements
in Dextrose Tryptone Agar. Dextrose is the carbohydrate source. Bromcresol
Purple is the pH indicator. Agar is the solidifying agent.


Formula / Liter


Enzymatic Digest of Casein
.................................................... 10 g


Dextrose
....................................................................................
5 g


Bromcresol Purple
............................................................... 0.04 g


Agar
........................................................................................
15 g


Final pH: 6.7 ± 0.2 at 25°C


Formula may be adjusted and/or
supplemented as required to meet performance specifications.


Precaution





1. For Laboratory Use.





Directions





1. Suspend 30 g of the medium
in one liter of purified water.





2. Heat with frequent agitation
and boil for one minute to completely dissolve the medium.





3. Autoclave at 121°C for 15
minutes.





Quality Control
Specifications


Dehydrated Appearance: Powder is homogeneous, free flowing, and light
green-beige.


Prepared Appearance: Prepared medium is purple and trace to slightly hazy.


Expected Cultural Response: Cultural response on Dextrose Tryptone Agar incubated
aerobically at 55 ± 2°C and examined for growth after 18 - 24 hours.