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Biological indicators for formalin sterilization

General

Formaldehyde is a chemical gas, an alkylating agent that can kill microorganisms by destroying proteins and nucleic acids.

Product description

SSI's biological indicators are microorganisms (spores of Geobacillus stearothermophilus, originally from ATCC 7953) prepared on filter paper as carrier material and packed in primary packaging consisting of transparent plastic film and paper that is permeable to gas and water vapour.

Formaldehyde indicators are produced in accordance with the standard EN ISO 11138-5 and are supplied with the following specifications: an initial microbial count of at least 10⁵ CFU/unit and a D‑value of at least 12 min. in a 1 mol/l solution of formalin at 60°C.

Use

Important factors for sterilisation with formaldehyde are gas concentration, relative air humidity and temperature. The sterilisation conditions can, for example, be 70 mg/l formalin, >90% relative humidity, and a temperature of 70°C. High relative humidity is crucial for killing microbes effectively. Due to the low sterilisation temperature, the process is intended for sterilisation of heat-sensitive instruments, e.g. endoscopes with sensitive optics, single-use medical equipment or implants. Formaldehyde has also been used to decontaminate cleanrooms and is used to a certain extent to decontaminate isolators and LAF benches, but, in this case, it can be difficult to maintain sufficiently high temperature and humidity.

The disadvantages of formaldehyde sterilisation are that it is hard to measure and therefore to control the physical parameters and to achieve adequate humidification. Moreover, formaldehyde is a carcinogen that irritates mucous membranes and can trigger allergies, and it is important to degas the products once sterilisation is complete. Because of the resulting uncertainty, SSI recommends that sterilisation testing with biological indicators be carried out for each individual sterilisation cycle. Biological indicators are also used for validation/revalidation.

Product range

The indicators are supplied in packs of 6. Subsequent culturing at Statens Serum Institut can be ordered separately.