A sterility indicating composition comprising a plurality of sterilization process resistant spores which contain an active protease during germination and initial outgrowth of the spores and a germination medium comprising at least one labeled protease substrate and at least one nutrient for germination of the spores wherein the medium is essentially free of a) any active protease other than the active protease contained by the plurality of spores and b) any protease substrate other than the at least one labeled protease substrate, other than any protease substrate originating from the plurality of spores, and other than any protease substrate which does not compete with the labeled protease substrate for the active protease and wherein the at least one labeled protease substrate comprises a peptide which can be cleaved by the active protease and which is labeled with one or more dye groups, at least one of which undergoes a detectable change when the peptide is cleaved by the active protease, and wherein the labeled protease substrate is stable at least at a temperature for incubating the spores, a sterilization process indicator comprising the composition, and a method of determining the effectiveness of a sterilization process using the composition and indicator are disclosed.
