Investigating the antimicrobial efficacy of two aerosolised hydrogen peroxide fumigation cycles for biological safety cabinet decontamination

AIMS: Fumigation of biological safety cabinets (BSCs) is essential for their safe use, maintenance and quality assurance of work performed. Hydrogen peroxide (HP) is frequently used as an alternative fumigant to formaldehyde, applied either at high concentrations (>30%) in vapour phase, or low concentrations (5-12%) as an aerosol (aHP). There is however limited evidence on the efficacy of low concentration aerosolised HP (aHP) fumigation to inactivate microorganisms within BSCs. This study evaluates the antimicrobial efficacy of aHP within a BSC III, comparing fumigation cycle parameters against a range of microorganisms. METHODS AND RESULTS: Biological indicators (BIs) were prepared by inoculating stainless steel coupons with either Geobacillus stearothermophilus spores, methicillin-resistant Staphylococcus aureus (MRSA) or Mycobacterium fortuitum. BIs were placed within a BSC III and fumigated with one or six diffusion cycles of aHP, with one diffusion cycle recommended for routine decontamination and six diffusion cycles advised for pre-maintenance decontamination, providing increased aHP quantity and exposure time. Fumigation with one aHP diffusion achieved a > 6 log10 reduction in G. stearothermophilus spore CFU, with 2.24 and 0.46 log10 average reductions for MRSA and M. fortuitum respectively. Six-diffusion fumigation achieved significantly reduced CFU counts for all microorganisms (average log10 reductions of 7.05, 5.25 and 5.26 for G. stearothermophilus, MRSA and M. fortuitum respectively). Incomplete BI inactivation was however observed for all microorganisms. CONCLUSIONS: Increased aHP diffusion cycles enhanced microbial reductions; however, complete elimination of microorganisms was not observed. BIs which represent likely contaminated microorganisms should be used when validating fumigation effectiveness.