The Principles of Medical Device Decontamination

Biological Indicators (BIs)

Biological Indicators are monitoring devices which contain living micro-organisms in the form of resistant bacterial spores. When used to monitor a sterilization process they provide a challenge to the process but are eventually killed in an effective process thereby demonstrating microbicidal lethality. Biological indicators therefore respond to all of the process variables of a sterilization process. Biological indicators come in many forms depending on how they will be used and are described in the BS EN ISO 11138 5 series of standards. • Seeded Product: Bacterial spores are inoculated onto the medical device which is to be sterilized. The device is then subjected to the proposed sterilization process and upon completion the medical devices are recovered and checked for spore survival. There should be none if an effective process has taken place. This method of utilisation is highly specialised and used extensively in the medical device and pharmaceutical manufacturing sector to help develop and prove process efficacy but is rarely if ever seen in healthcare. • Suspensions of spores in ampoules: Bacterial spores are suspended in liquid growth medium with an indicator dye. These ampoules would be used to develop or validate processes used to sterilize contained fluids such as intravenous injections. After processing the ampoules would be recovered and directly incubated. Such presentations must not be used to estimate process lethality in saturated steam sterilization processes used to sterilize surfaces because the ampoules will not detect whether or not moist heat conditions are present. • Spore Strips: Bacterial spores are impregnated onto strips of, usually, filter paper. The spore strips are usually contained in a glassine envelope. Spore strips would be placed at a position within a medical device or medical device load which is then exposed to the process. After processing the spore strips are recovered and dropped into a container of nutrient medium and then incubated to see if there are any survivors. It is vital post processing recovery of spore strips is carried out using strict aseptic technique to avoid accidental contamination and false positives.

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