POTATO DEXTROSE AGAR OXOID

POTATO DEXTROSE AGAR (EP/USP/JP/BP)

Code: CM0139

for the detection and enumeration of yeasts and moulds in butter and other dairy and food products

Also for the preparation of Aspergillus niger for the Harmonised Microbial Limit Tests from EP/USP/JP (enumeration test)

Formula	gm/litre
Potato extract	4.0*
Glucose	20.0
Agar	15.0
pH 5.6 ± 0.2 @ 25°C

Description

Food
A suitable medium for the isolation and count of yeasts and moulds in dairy products¹or those occurring on the surface of fresh meats, cured meats and sausage products and other foods². This medium is suitable for the detection and enumeration of heat resistant moulds in thermally processed fruits and fruit products².

Work carried out in cooperation with CSIRO Melbourne had shown that the minerals present in agar could influence the pigment formation of certain fungi. Where pigment production is a critical part of the identification of the fungus it is clearly important to stabilise this characteristic. The agar used in Potato Dextrose Agar is carefully screened to ensure correct pigment production by fungi such as Fusaria spp.

Pharma
A suitable medium for the preparation of Aspergillus niger. Potato Dextrose Agar conforms to the parameters of the harmonised Microbial Limit Tests from EP/USP/JP (enumeration test)^3,4,5,.

Technique

Food
After sterilising the reconstituted medium adjust the reaction to pH 3.5 by adding 1ml of Lactic Acid 10% (SR0021) to each 100ml of medium at 50°C. Do not reheat after acidification. Prepare dilute emulsions or suspensions of the product to be tested, make pour-plates in the usual manner, and incubate for 5 days at 21°C. Count the number of yeast and mould colonies.

Pharma
Grow Aspergillus niger on Potato Dextrose Agar (CM0139) at 20-25°C for 5-7 days or until good sporulation is achieved.

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 medium at 2-8°C.

Appearance
Dehydrated medium: Off-white, free-flowing powder
Prepared medium: Light straw coloured gel

Quality Control

Food
Compare with previous lot/batch using pasteurised and raw milk samples, incubated at 32-35°C for 48 hours.

Positive control:	Expected result
Aspergillus fumigatus ATCC® 9197 *	White mycelium, blue green spores
Negative controls:
Uninoculated medium	No change
At pH 3.5 Bacillus subtilis ATCC® 6633 *	No growth