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Population determination of biological indicators

1. Aseptically extract 10 unexposed spore strips from their glassine envelopes and place them within 100 ml sterile chilled water in a sterile high speed blender. Homogenise 3-5 min until no large particles are visible. Homogenisation with a glass-bed may result in a lower CFU-count, due to insufficient homogenisation. Available spore suspensions can be used directly after shaking well. If the spores were exposed to formaldehyde, they have to be pre-treated to inactivate resident formaldehyde particles. The formaldehyde residues would hamper the outgrowth of the spores. Therefore, the sterilized spore strips are aseptically transferred to Na2SO3 solution (2 %, 10 ml, 10 min) and heat activated (90-93