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Fungal propagules in house dust. I. Comparison of analytic methods and their value as estimators of potential
A P Verhoeff1, E S van Reenen-Hoekstra, R A Samson
1Department of Environmental Medicine, Municipal Health Service, Amsterdam, The Netherlands.
Abstract:
The presence of viable mold propagules in house dust was investigated by 10 different analytic methods, in order to determine to what extent different results are obtained when different analytic methods are used. Moreover, the value of this measurement as an estimator of the potential exposure to fungi in epidemiologic studies was assessed. Floor and mattress dust was sampled in 60 homes in The Netherlands during autumn 1990. For investigation of the variability in time, sampling was repeated in 20 homes after 6 weeks. Each analytic method is characterized by a unique combination of culture medium, suspension medium, and dilution step. The highest mean number of colony-forming units (CFU)/g dust was obtained by suspension of at least 100 mg dust in a peptone or sucrose solution in a ratio of 1:50 (w/w), followed by 10-fold dilution and plating on DG18 agar (geometric mean (GM) approximately 60,000 CFU/g dust). The lowest mean number of CFU/g dust was obtained by direct plating of 30 mg dust on V8 agar (GM approximately 5300 CFU/g dust). The mean coefficient of variation of duplicate analyses varied from 11%, for suspension in sucrose and plating on DG18 agar, to 27%, for suspension and dilution in sucrose in combination with V8 agar. The highest mean number of species isolated was obtained by direct plating of 30 mg dust on DG18 agar (mean number of species: 17). Suspension and dilution on DG18 or V8 agars yielded an average of approximately six species. In duplicate analyses, the mean percentage of agreement for the species isolated varied from approximately 35%, for suspension and dilution, to 60%, for direct plating.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
This study compared 10 methods for measuring mold propagules in house dust. The best method for quantifying mold colony-forming units (CFU) involved specific suspension and plating techniques on DG18 agar.
Area of Science:
- Environmental Health
- Microbiology
- Analytical Chemistry
Background:
- House dust can contain viable mold propagules, posing potential health risks.
- Accurate quantification of mold exposure is crucial for epidemiological studies.
- Variability in analytical methods can affect results and exposure estimations.
Purpose of the Study:
- To investigate the variability of results obtained from 10 different analytical methods for mold propagule detection in house dust.
- To assess the value of mold quantification in house dust as an estimator of potential fungal exposure in epidemiological research.
Main Methods:
- Sampling of floor and mattress dust from 60 homes, with repeat sampling in 20 homes after 6 weeks.
- Characterization of 10 analytical methods based on unique combinations of culture medium, suspension medium, and dilution steps.
- Quantification of colony-forming units (CFU) per gram of dust and identification of fungal species.
Main Results:
- The highest mean CFU/g dust (approx. 60,000) was achieved using suspension in peptone/sucrose (1:50 w/w), 10-fold dilution, and plating on DG18 agar.
- Direct plating of 30 mg dust on V8 agar yielded the lowest mean CFU/g dust (approx. 5300).
- Direct plating on DG18 agar isolated the highest mean number of species (17), while suspension/dilution methods yielded fewer species (approx. 6).
Conclusions:
- Methodological choices significantly impact the quantification of mold propagules and species diversity in house dust.
- Specific methods, particularly suspension in peptone/sucrose with DG18 agar, provide higher CFU counts.
- Direct plating on DG18 agar offers a broader spectrum of species identification, which may be valuable for exposure assessment.