Comparison of Ion Plasma, Vaporized Hydrogen Peroxide, and 100% Ethylene Oxide Sterilizers to the 12/88 Ethylene Oxide Gas Sterilizer

Abstract

Objective: The performance of a standard gas sterilizer, which uses a mixture of 12% ethylene oxide (EtO) and 88% chlorofluorocarbon as the sterilizing gas (12/88), was compared to selected gas, ion plasma, and vaporized hydrogen peroxide ($H_{2}O_{2}$) sterilizers that do not use chlorofluorocarbons. The effect of serum and salt on sterilizer performance was evaluated. Design: Test carriers (porcelain and stainless steel penicylinders, or 125-cm lengths of plastic tubing [internal diameter of 3.2 mm]) were inoculated with Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, Mycobacterium chelonei, Bacillus stearothermophilus spores, Bacillus subtilis spores, and Bacillus circulans spores and then subjected to sterilization using 12/88, 100% EtO, ion plasma, or vaporized $H_{2}O_{2}$. The bacterial inoculum was prepared with and without 10% serum and 0.65% salt, and the residual bacterial load after sterilization as determined using viable counts. Results: All of the sterilizers tested effected a $six-log_{10}$ reduction of the bacterial inoculum on penicylinders, unless 10% serum and 0.65% salt were present, in which case the 100% EtO, vaporized $H_{2}O_{2}$, and ion plasma sterilizers were not as effective as the 12/88 sterilizer. None of the sterilizers could eradicate $10^{6}$ CFU of all of the bacteria in 10% serum and 0.65% salt when inoculated inside a narrow lumen. Conclusions: The margin of safety for the 100% EtO, vaporized $H_{2}O_{2}$, and ion plasma sterilizers is less than that of the 12/88 sterilizer. The inability of all sterilizers, including the 12/88, to kill organisms in narrow lumens reliably when serum and salt were present raises concern about the current practice of gas sterilization of flexible endoscopes.