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Evaluation of Microbial Growth and Survival on Construction Materials Treated with "Microbial Shield"

Test Conditions

In order to test the ability of Microbial Shield agent to deflect microbial growth, construction materials was treated with the Microbial Shield agent and inoculated with high titer stocks (10⁷-10⁸) of the test microorganisms. Control sample were also inoculated with same numbers of test microorganisms. Inoculated samples were placed in tightly sealed polyethylene containers. The samples inoculated with fungal mycelium and bacterial cell were incubated under >90% relative humidity. Whereas, samples inoculated with fungal spores were incubated under <30% relative humidity. The inoculated samples were incubated at 37°C and 28°C. Treated material was aged in the environmental chambers for a designated period of time (8 weeks for fungi and 2 weeks for bacteria). Samples were periodically removed from incubation chambers and analyzed for microbial growth and viability.  

Microbial Growth and Viability Assay

The samples inoculated with fungal mat (mycelium) were monitored every other day for visible mold growth (Figures 2, 3, and 4). The percent surface area covered by the growth of Penicillium and Stachybotrys was visually appreciated. The samples inoculated with fungal spores were assayed for spore viability after 30, 60 and 75 days of incubation at specified temperatures. Fungal spores were recovered using glycine elution buffer and spores were tested for viability using hanging drop method. Briefly, the recovered spores were suspended in a drop of water and deposited on a glass slide. The glass slide was incubated in humidity chamber in inverted position. The number of germinated spores were counted using microscope.   

The samples inoculated with bacterial cells were assayed for bacterial cell viability on day 0, 1, 2, 3, 4, 5, 7, 9, 11, 13, and 15. Bacterial cells were recovered using glycine elution buffer and were tested for viability using membrane filtration on selective medium (Figure 5). 

RESULTS

The mold growth data for samples inoculated with fungal mycelium is presented in Figures 6 and 7. Untreated drywall and pinewood coupons incubated at 37°C and 28°C, showed profuse growth of Penicillium and Stachybotrys after 75 days of incubation, resulting.

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