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 Evaluation of Fungal Growth on Icynene Foam Insulation


Dr. David C. Straus, PhD.
Enusha Karunasena, M.S.


Texas Tech University Health Sciences Center
Department of Microbiology and Immunology
3601 4th Street Lubbock, TX 79430


October 5, 2001

 

Introduction and Materials & Methods

One building material product was evaluated to determine whether Stachybotrys and Penicillium fungal growth could be supported on the surface of these items. The building material sample consisted of a piece of foam insulation. A series of experiments were conducted with the insulation to mimic conditions that would promote “sick” building syndrome.

Insulation Sample. The bulk sample of insulation was cut into squares 5cm x 5cm. A total of three sections were examined in triplicate, each section received Stachybotrys chartarum spores or Penicillium chrysogenum spores. The samples were sterilized prior to testing by autoclaving. The samples were placed into sterile glass jars. Each sample was inoculated with 20ml sterilized water, to mimic a watering event. Fungal spores were harvested with sterile phosphate-buffered saline solution (PBS) and counted on a hemacytometer. The spore counts for both Stachybotrys and Penicillium were adjusted to 1 x 105 spores/ml of solution. A total of 1ml of spore solution was added onto the surface of each of the building materials. Tryptic soy broth (TSB) was utilized as a food source for these experiments, each of the 3 samples in a set received 0?, 250?, or 500? of TSB. The samples were incubated in a disinfected chamber at 25?C, at a relative humidity of 54%. Each sample was evaluated for fungal spore viability at zero time and after a 15-day incubation period.

Each of the insulation samples for both the zero-time incubation and the 15-day incubation were washed individually with 10ml of sterile water. Each insulation section was placed in a sterile 50ml centrifuge tube with 10ml of sterile water. The samples were placed on a vortex for approximately 5 minutes to agitate the fungal spores off of the insulation and into the 10ml water. A series of 1:10 dilutions were made with the harvested solution from washing the insulation. The dilutions were plated onto potato-dextrose agar (PDA) plates in duplicate and placed in an incubator at 25?C, for 3-5 days, at a relative humidity of 54%. A spore count was determined based on the number of viable spores that germinated on the PDA plates.

A one-way analysis of variance (ANOVA) was used to test the significance of difference in growth of the two fungi on the surface of the insulation. A Student-Newman-Keuls test was employed to test the significance between the zero time set of insulation sections to the samples that were incubated for 15 days. A P value of less that 0.05 was the minimum level of significance. Fungal concentrations were reported as the mean ? standard deviation.

 

Results

Each of the insulation sections received 1 x 105 sp/ml of either Stachybotrys chartarum spores or Penicillium chrysogenum spores. At zero time spores were harvested off of the surface of the insulation to determine the viability of the spores. The Stachybotrys spores inoculated onto the insulation samples that did not receive a food source had 1.5 x 102 sp/ml that were viable, after the 15-day incubation period 5.5 x 101 sp/ml were viable. Samples that received 250? of TSB had 1.5 x 102 sp/ml that were viable, and at the end of the 15-day incubation period there was 3.6 x 102 sp/ml, an increase in the number of viable spores. Similar to the samples with 250? of TSB the samples that were inoculated with 500? of TSB had an increase in the number of viable spores harvested from zero time at 2.2 x 102 sp/ml to 6.3 x 103 sp/ml.


Conclusions

Based on the results that were obtained from this study there are several conclusions that can be made. The results suggest that this insulation material cannot be utilized as a food source itself by fungi. The insulation was able to support both Stachybotrys and Penicillium growth after a wetting event with the addition of a food source. The insulation material did not affect fungal spore viability of both Stachybotrys and Penicillium fungal spores without a food source after a watering event.

 


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