Description
Shahidi and Ferguson1 developed SFP agar using Kanamycin Sulphate at 12mgm/litre and Polymixin B Sulphate at 30,000 IU/Litre in order to convey a high degree of selectivity for Clostridium perfringens and other strains of sulphite reducing clostridia to the medium.
Comparative studies of SFP medium with Tryptose Cycloserine Agar (TSC agar) and Sulphadiazine Polymixin agar (SPS agar), have demonstrated that, while SFP agar allows a greater recovery of spores and vegetative cells of Cl.perfringens than other media, the inhibition of enterococci, coliforms and Proteus sp. Is not as effective2,3.
The sulphite reducing properties of Clostridium perfringens and some other members of the genus Clostridia produce black colonies in the presence of Sodium metabisulphite and Ferric ammonium citrate, as the sulphite is reduced to sulphide and combine with the iron salt to form black ferric sulphide. Black colonies of Cl. perfringens are usually surrounded by a halo caused by their lecithinase activity on the egg yolk in the medium. However, not all strains of Cl. perfringens are lecithinase positive, and confirmatory testing of all black colonies on SFP agar should be performed. It should also be noted that lecithinase positive strains of some facultative anaerobes growing on SFP agar may interfere with the recognition of lecithinase positive strains of Cl. perfringens. Omission of egg yolk in the medium, while removing a nutrient and an identification marker, may be advantageous in that the smaller colonies resulting allow for easier enumeration in the presence of large numbers of Cl. perfringens in the sample.
Supplied in box of 10 x 100gm vials.
