SCA in the prestudy was prepared by adding glucose and sodium azide to perfringens agar base (Oxoid). SCA in the collaborative trial was prepared from its individual ingredients. Both SCA media differ in their concentration of elective substances: SCA from the prestudy contains 1 g/l ammonium iron (III) citrate and 1 g/l Na2S2O5, and SCA from the collaborative trial contains 0.5 g/l of both compounds. Dilutions were made with reduced saline solution (RSS) containing NaCl (8 g/l) and cysteine–HCl (0.5 g/l).