A study published by the UK Health Protection Agency highlights the fact that MRSA dried on surfaces appears to be less susceptible to hydrogen peroxide vapour (HPV) than bacterial endospores in the form of commercially produced biological indicators. This is a surprise because bacterial endospores are generally considered to be close to the top of the tree in terms of resistance to disinfection and sterilization. The answer lies in the enzyme catalase. Catalase breaks down hydrogen peroxide and is produced by MRSA but not by the metabolically inert spores. A previous study also showed that catalase-producing bacteria were less susceptible to HPV than bacteria that did not produce catalase and metabolically inert spores.

Bacterial endospore biological indicators (BIs) are typically used to monitor the efficacy of HPV systems. Does the finding that MRSA and probably other catalase-producing bacteria are less susceptible to HPV, “cell for spore”, than bacterial endospores challenge the use of BIs to monitor decontamination using HPV? In vitro susceptibility is important, but the resistance of a ‘system’ to HPV will be determined by a number of factors including the relative susceptibility of the organisms, suspending medium, substrate and inoculum. Thus, you’ll never get a “one-size-fits-all” monitoring system for HPV. BIs provide a stringent, repeatable, consistent and safe method to monitor the efficacy of HPV. Whilst they may not be top of the tree in terms of efficacy, BIs provide a useful yard-stick for monitoring efficacy.

Article citation: Pottage T, Macken S, Walker JT, Bennett AM. Meticillin-resistant Staphylococcus aureus is more resistant to vaporized hydrogen peroxide than commercial Geobacillus stearothermophilus biological indicators. J Hosp Infect 2012; 80:41-5.