Description
Amyl Media Perfringens Agar Base (OPSP), AM 152, is based on the formulation of Handford1 who, recognizing the problems associated with the identification and enumeration of Cl.perfringens in foodstuffs, developed a buffered, egg free selective mediium more suitable for the purpose.
The medium contains nutrients and growth factors in the form of peptones, liver extract and yeast extract. Tris(2-amino-2(hydroxymethyl)-propane-1,3-diol) provides a buffering system while sodium metabisulphite and ferric ammonium citrate are present in order to detect sulphite reducing bacteria which produce H2S, manifested by the formation of black, iron sulphide containing colonies.
Selectivity of the medium for Cl.perfringens is achieved by the presence of 100 μg/ml of Sulphadiazine (Supplement SP 456/1) and 0.5 μg/ml of Oleandomycin plus 10 IU per ml of Polymixin B (Supplement 456/2), which inhibit the growth of other sulphite reducers, particularly members of the Proteus and Citrobacter genera., as well as the majority of gram negative organisms together with gram positive organisms such as Staphyloccus sp. and Bacillus sp. Other sulphite reducing anaerobes such as Cl.bifermentans, the presence of which could interfere with detection and enumeration of Cl.perfringens, are also inhibited. Not inhibited are Enterccocci, which appear as small white colonies, easily distinguishable from the black colonies formed by Cl.perfringens.
