The Influence of Humidity, Hydrogen Peroxide Concentration, and Condensation on the Inactivation of Geobacillus stearothermophilus Spores with Hydrogen Peroxide Vapor

Abstract

The study presented here examined the factors influencing the effectiveness of surface decontamination with hydrogen peroxide vapor. The impact of relative humidity and hydrogen peroxide gas concentrations was investigated and compared to a dew point analysis of these various sterilant atmospheres. For this purpose, a series of different H 2 O 2 decontamination cycles were developed and tested for antimicrobial effectiveness using biological indicators inoculated with greater than 10 6 spores of Geobacillus stearothermophilus. The results indicate that an increasing concentration of hydrogen peroxide in the gas phase and higher humidity levels result in a faster inactivation of the test organisms. The higher the H 2 O 2 gas phase concentration was, the more independent the inactivation effect from the humidity level. At lower H 2 O 2 concentrations, the same kill was achieved with higher humidity. Subvisible condensation was found to be necessary for short inactivation times, but condensation in the visible range did not further enhance the sporicidal activity. The molecular deposition of water and hydrogen peroxide on the target surface represents the determining factor for microbial inactivation, whereas the hydrogen peroxide concentration in the gas phase is of secondary importance.

Vapor Phase Hydrogen Peroxide – Method for Decontamination of Surfaces and Working Areas from Organic Pollutants

“…This theory is supported by theoretical and experimental analysis which clearly show that condensation, and mainly "microcondensation" (i.e. non-visible condensation in small amounts), are key and critical parameters for quick and reproducible inactivation of microorganisms by VPHP (Unger-Bimczok et al, 2008). Condensation (preferred by Bioquel (Fisher & Caputo, 2004)) in case of the "wet" VPHP process is the basic requirement of the technology.…”

“…Current literature data (Chung et al, 2008;Unger-Bimczok et al, 2008;U.S. Environmental Protection Agency, 2005) indicate that the VPHP process is a multi-parameter problem, the effectiveness of which is mainly influenced by the concentration of gaseous hydrogen peroxide, temperature, relative humidity, and condensation of hydrogen peroxide on the decontaminated surfaces.…”

“…The decontamination cycle based on biocidal properties of VPHP meets this requirement. There are two different ideas about how to carry out the surface decontamination with VPHP (Fisher & Caputo, 2004;Unger-Bimczok et al, 2008;Watling et al, 2002). The traditional one prefers to perform the decontamination under "dry" conditions without condensation of hydrogen peroxide or water (preferred by Steris (Fisher & Caputo, 2004)).…”

“…Condensation is unwanted because of corrosion of many materials and prolonged aeration time. The process is not under control and thus in case of condensation the decontamination is not homogeneous (Unger-Bimczok et al, 2008;Watling et al, 2002). In case of the "dry" way of the VPHP process, decontamination of closed indoor spaces and surfaces or quick inactivation of contaminants due to high concentration of hydrogen peroxide vapors is quickly achieved.…”

“…Similarly as in its liquid solution, hydrogen peroxide also has sterilization properties in the vapor phase against vegetative bacteria and highly resistant bacteria endospores (Block, 1991;French et al, 2004;Hall et al, 2007;Johnston et al, 2005;Kahnert et al, 2005;Klapes & Vesley, 1990;Kokubo et al, 1998;Rogers et al, 2005;Sapers et al, 2003;Unger-Bimczok et al, 2008), viruses (Heckert et al, 1997), fungi (Forney et al, 1991), yeast, amoebae, infective proteins and other microorganisms (Fichet et al, 2004;Klapes & Vesley, 1990;Vassal et al, 1998). As a model organism for the validation, Bacillus stearothermophilus ( Geobacillus stearothermophilus) which is mainly deposited on stainless steel is commonly used (Block, 1991;Bounoure et al, 2006;Chung et al, 2008, Fisher & Caputo, 2004Johnston et al, 2005;Klapes & Vesley, 1990;Unger et al, 2007).…”