T.S.C. Agar Base (Tryptose Sulfite Cycloserine) was originally formulated by Harmon for presumptive identification and enumeration of Clostridium perfringens from food. This media is the most useful media for the quantitative recovery of C. perfringens while suppressing the growth of other facultative anaerobes. It is recommended by ISO Normative Committee and depending on the formula, the supplements added can increase the selectivity of the medium.

Egg Yolk Emulsion (Cat. CL-5152) supplement is added for the demonstration of lecithinase activity, and after incubation, lecithinase-producers produce an opaque area in the colony surroundings. The superior nutrient base has the optimal conditions for the development of Clostridia. Tryptose and soy peptone provide nitrogen, vitamins, minerals, and amino acids essential for growth. Yeast extract is source of vitamins, particularly the B-group, essential for bacterial growth. Ferric ammonium citrate and disodium disulfite are H2S indicators. Bacteriological agar is the solidifying agent.

Cycloserine inhibits the accompanying bacterial flora which can cause colonies that develop to remain smaller. Colonies producing hydrogen sulphide are characterized by a blackening due to the reaction with the ferric salt. The degradation of the egg yolk lecithin produces insoluble products which accumulate around the colonies, forming a white precipitate. After 24 hours incubation, all black colonies, lecithinase positive as well as the lecithinase negative ones, must be considered as positive presumptive C. perfringens and the corresponding confirmation tests must be made.