Evaluation of Biological Indicator Spores as Tools for Assessment of Fumigation Decontamination Effectiveness

In high-containment laboratories and animal facilities common practice is to decontaminate the facilities prior to maintenance or in an emergency situation. Many laboratories use commercially available biological indicators (BIs) to validate the decontamination procedure. In this study the focus was to evaluate the reliability of four different commercial BIs in comparison to control microorganisms that are commonly used in laboratories. Two different fumigation decontamination procedures were chosen: formaldehyde (FA) and vaporized hydrogen peroxide (VHP). The control microorganisms were Salmonella typhimurium, Brucella melitensis, Bacillus thuringiensis spores, porcine parvovirus, equine rhinitis A virus, bovine viral diarrhea virus, and low pathogenic avian influenza virus.

Exposure to formaldehyde caused a sufficient reduction of all the control microorganisms, including B. thuringiensis spores, whereas only one of the four commercial BIs was completely negative for growth. The VHP decontamination procedure was not able to reduce any of the control microorganisms more than 4 log₁₀, except for the enveloped viruses, whereas the BIs with the lowest concentration (10⁵ microorganisms per spore strip) indicated a satisfactory decontamination procedure.

These results indicate that commercial BIs could be unreliable as general indicators of decontamination effectiveness. To ensure a reliable decontamination process, BIs have to be evaluated for each protocol in parallel with the microorganisms used in the laboratory.