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Evaluation of methods for enumerating microorganisms in filter samples from highly contaminated occupational
W Eduard1, J Lacey, K Karlsson
1National Institute of Occupational Health, Oslo, Norway.
American Industrial Hygiene Association Journal
|August 1, 1990
Summary
Different microscopy techniques (SEM, LM, FM) and culture were compared for air microorganism analysis. Scanning electron microscopy and light microscopy generally provided similar counts, except in pig houses where epifluorescence microscopy detected more bacteria.
Area of Science:
- Environmental microbiology
- Microscopy techniques
- Air quality assessment
Background:
- Accurate enumeration of airborne microorganisms is crucial for assessing workplace contamination.
- Various microscopy methods and culturing techniques exist, each with potential limitations in sensitivity and specificity.
- Understanding the comparability of these methods is essential for reliable environmental monitoring.
Purpose of the Study:
- To compare the effectiveness of scanning electron microscopy (SEM), light microscopy (LM), epifluorescence microscopy (FM), and culturing for enumerating airborne microorganisms.
- To evaluate the impact of different working environments on the accuracy of these methods.
- To determine the viability of detected microorganisms and assess potential biases in counting methods.
Main Methods:
- Parallel air sampling using membrane filters in diverse, contaminated work environments.
- Microorganism enumeration via SEM, LM, FM, and traditional culture methods.
- Analysis of microorganism types (bacteria, actinomycetes, fungal spores) and aggregate sizes.
Main Results:
- SEM and LM provided similar microorganism estimates, except in pig houses where FM detected additional bacteria on skin scales.
- Culture counts were consistently lower than SEM/LM, with variable results compared to FM.
- Viability estimates ranged from 0.1-68% for bacteria/actinomycetes and 3-98% for fungal spores.
- Log-normal distribution observed for spore types, with potential underrepresentation of single bacteria/actinomycetes and small aggregates.
- SEM and LM showed higher precision for counting spore-containing particles compared to individual spores.
Conclusions:
- SEM and LM are reliable for general microorganism counts in air samples, with LM being more cost-effective.
- FM offers advantages in specific environments like pig farms for detecting bacteria on surfaces.
- Culturing provides viability data but may underestimate total counts due to aggregate formation and sampling biases.
- Careful consideration of counting strategies (e.g., systematic field distribution) is needed for direct microscopy methods to account for particle deposition patterns.