Biological indicators for the control of ethylene oxide sterilization.

A new biological indicator has been developed for the control of ethylene oxide sterilization, particularly for large scale sterilization of disposable medical equipment. The aim has been to provide the new indicator with the same resistance to the combined effect of ethylene oxide and water vapour as the biological indicator referred to by the health authorities in Scandinavia. The reference indicator contains spores of a Danish test strain, Bacillus subtilis, in sand. The new one contains spores of a test strain used extensively for biological indicators, viz. B. subtilis var. niger (B. globigii). The spores in the new preparation are dried in pieces of cotton yarn. The two indicators were exposed to ethylene oxide and water vapour in five different series of experiments and almost the same resistance was found. In simulated routine sterilization procedures, the new indicator was placed at locations not easily accessible for the gas and water vapour, and the results reflected the blockage of diffusion. The experiments included samples of household dust. The resistance of the microorganisms in the dust was compared with that of the biological indicators. Based on these comparisons, it is concluded that the resistance of the two biological indicators to ethylene oxide is in accordance with the official Scandinavian standard for sterilized medical equipment when used in the control of sterilization of products with low microbial contamination.