A sterilization indicator, including a first compartment containing a genetically engineered biological indicator, and a second compartment containing an enzyme substrate, the second compartment adapted to maintain the enzyme substrate separate from the biological indicator during sterilization, and to permit the enzyme substrate to contact the biological indicator after the biological indicator has been exposed to the sterilization medium; in which the genetically engineered biological indicator comprises at least one test organism and at least one reporter gene suitable for producing an indicator enzyme, the reporter gene being taken up by the test organism; and the test organism is free of any active or activatable repressor gene that would inhibit expression of the reporter gene if present in the test organism or sterilization indicator, and the indicator enzyme and the enzyme substrate are selected such that enzymatic action of the indicator enzyme upon the enzyme substrate yields a detectable signal.