Generally, chemical methods achieve only disinfection (see below); the use of the gas ethylene oxide, however, is effective against bacteria, their spores and viruses. It is used for sterilising large items of medical equipment, and materials such as plastics that would be damaged by heat treatment. Ethylene oxide is particularly effective in sterilising items such as dressings and mattresses, due to its great powers of penetration. In the food industry, it is used as an antifungal fumigant, for the treatment of dried fruit, nuts and spices. The materials to be treated are placed in a special chamber which is sealed and filled with the gas in a humid atmosphere at 40-50 °C for several hours. Ethylene oxide is highly explosive, so it must be used with great caution; its use is rendered safer by administering it in admixture (10 per cent) with a non-flammable gas such as carbon dioxide. It is also highly toxic, so all items must be thoroughly flushed with sterile air following treatment to remove any trace of it. Ethylene oxide is an alkylating agent; it denatures proteins by replacing labile hydrogens such as those on sulphydryl groups with a hydroxyl ethyl radical (Figure 13.4).
We saw at the beginning of this chapter how sterilisation is an absolute term, implying the total destruction of all microbial life. Disinfection, by comparison, allows the possibility that some organisms may survive, with the potential to resume growth when
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