PRE-SUPPLEMENTED DG18 (ISO) AGAR

Specifications

Description
Pre-supplemented Dichloran-Glycerol (DG18) (ISO) Agar is a dehydrated culture medium formulated according to BS ISO 21527-2: 2008 Microbiology of food and animal feeding stuffs – Enumeration of yeasts and moulds Part 1- Colony counting technique in products with less than or equal to 0.95 water activity¹. It is recommended for the enumeration and isolation of xerophilic moulds from dried and semi-dried foods. Examples of these are dried fruits, spices, confectionery, cereals, nuts and dried meat and fish products.

The medium formulation contains glycerol at 18% (w/w) which lowers the water activity (a_W) from 0.999 to 0.95. The medium also contains Chloramphenicol at 0.1g/L as per the ISO 21527-2 formulation. The addition of this antibiotic into the powder aids in reducing hamful chemical handling in the laboratory and provides an agar medium that only needs glycerol adding. The medium also contains Dichloran which inhibits spreading of mucoraceous fungi and restricts the colony size of other genera. This restrictive characteristic makes the medium especially suitable for enumeration because it allows growth of background organisms, which form only small colonies, not obscuring mould or yeast identification and enumeration. In a comparative study carried out between DG18 and DRBC, (a medium of higher a_W) greater recovery of xerophilic moulds was achieved on the DG18 medium¹. In this study it was found that two of the fungi commonly isolated from dried foods in high numbers, Aspergillus penicilloides grow very poorly or not at all on DRBC.