Importance of considering injured microorganisms in sterilization validation

Disinfection or sterilization treatment by heating, irradiation, or chemicals can cause injury to microorganisms at sublethal levels. Microbial injury is the inability to grow under conditions suitable for the uninjured microorganisms. This inability of injured microorganisms to grow is explained in terms of more complex or different nutritional requirements or in terms of increased sensitivity to environmental conditions such as incubation conditions (time or temperature) or to chemical agents such as halogen compounds. Injured microorganisms can be distinguished from those that are dead or mutated by their ability to regain normal physiological activity when placed in appropriate conditions for cultivation. The return to normal physiological function has been termed repair. The extent and severity of sublethal injury, the mechanisms of injury, and the mechanisms and degree of recovery vary with the sterilization procedures, the species, the strains, the condition of the microorganism, and the methods of repair. Injury to spore formers has been detected at different stages of the spore cycle. The sites of injury include damage to enzymes, membrane disruption, and/or damage to DNA or RNA. Information on the sublethal injury and recovery of microorganisms is very important in evaluating sterilization/disinfection procedures. This paper supplies academic as well as practical information dealing with the repair, and detection of injured microorganisms for performing reproducible sterilization validation.