Biological indicators are used to monitor and evaluate the effectiveness of sterilization. They are designed for use with ethylene oxide gas, dry heat, steam or radiation. Ethylene oxide gas is used to kill bacteria, mold and fungi in medical supplies such as bandages and food stuffs such as spices. Dry-heat sterilization uses an oven to raise the temperature of items that are wrapped in foil or fabric. Steam sterilization uses an autoclave, a self-locking machine that sterilizes its contents with steam under pressure. Biological indicators that are suitable for use with gamma and electron beam radiation techniques are also available.
Biological indicators are available in many different forms. Examples include strips, discs, suspensions, test tubes and ampoules. Spore strips are biological indicators that are packaged in a pouch made of glassine, a paper that is resistant to moisture and air at ambient temperatures and pressures. Spore discs are usually made of borosilicate paper or stainless steel. Spore suspensions are diluted aliquots that are derived from a primary batch of spores. Test tubes are available in a variety of sizes and are usually made of expansion-resistant glass. Ampoules are small, self-contained, vials which are hermetically sealed with a flame. They have a score mark around the neck so that the sealed top can be snapped off by hand. Typically, ampoules are used to contain hypodermic injection solutions.
Specifications for biological indicators vary by product form and may carry different certifications. For example, spore strips and spore discs are specified in terms of shelf life, strip size, and package size. Specifications for spore suspensions include quantity, population, culture media, incubation period and temperature. Spore strips, ampoules and suspensions at common population levels are often provided with multiple certifications that include D value confirmation, survival/kill analysis and population verification. Biological indicators that meet US Pharmacopoeia (USP) standards are also available.