Large particles are responsible for elevated bacterial marker levels in school air upon occupation
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Published on: July 12, 2024
Alvin Fox1, William Harley, Charles Feigley
1Department of Environmental Health Sciences, Arnold School of Public Health, University of South Carolina, Columbia, SC 29208, USA.
Abstract:
Muramic acid (Mur) is found in bacterial peptidoglycan (PG) whereas 3-hydroxy fatty acids (3-OH FAs) are found in Gram-negative bacterial lipopolysaccharide (LPS). Thus Mur and 3-OH FAs serve as markers to assess bacterial levels in indoor air. An initial survey, in a school, demonstrated that the levels of dust, PG and LPS (pmol m(-3)) were each much higher in occupied rooms than in the same rooms when unoccupied. In each instance, the Mur content of dust was increased and the hydroxy fatty acid distribution changed similarly suggesting an alteration in the bacterial population. Here, findings are compared with results from two additional schools. Follow-up aerosol monitoring by particle size was also performed for the first time for all 3 schools. The particle size distribution was shown to be quite different in occupied versus unoccupied schoolrooms. Within individual classrooms, concentrations of airborne particles [greater-than-or-equal]0.8 [micro sign]m in diameter, and CO(2) were correlated. This suggests that the increased levels of larger particles are responsible for elevation of bacterial markers during occupation. Release of culturable and non-culturable bacteria or bacterial aggregates from children (e.g. from flaking skin) might explain this phenomenon.
Insights
Bacterial markers like muramic acid and 3-hydroxy fatty acids increase in occupied schoolrooms. Larger airborne particles, potentially from children, correlate with these elevated bacterial levels.
Area of Science:
- Environmental microbiology
- Indoor air quality assessment
Background:
- Bacterial peptidoglycan (PG) contains muramic acid (Mur), and Gram-negative lipopolysaccharide (LPS) contains 3-hydroxy fatty acids (3-OH FAs).
- These compounds serve as biomarkers for quantifying bacterial presence in indoor environments.
Purpose of the Study:
- To compare bacterial marker levels (Mur, 3-OH FAs) in occupied versus unoccupied schoolrooms across three schools.
- To investigate the relationship between airborne particle size distribution and bacterial marker concentrations.
Main Methods:
- Measurement of muramic acid and 3-hydroxy fatty acids in dust and aerosols.
- Particle size distribution analysis of airborne particles.
- Correlation analysis between particle counts, CO2 levels, and bacterial markers.
Main Results:
- Significantly higher levels of PG and LPS were found in occupied schoolrooms compared to unoccupied ones.
- Elevated Mur content and altered hydroxy fatty acid profiles indicated changes in bacterial populations during occupation.
- Airborne particle size distributions differed between occupied and unoccupied rooms, with larger particles ([greater-than-or-equal]0.8 μm) correlating with increased bacterial markers and CO2.
Conclusions:
- Occupancy in schoolrooms leads to increased airborne bacterial markers, likely associated with larger particle concentrations.
- Children may contribute to elevated bacterial markers through the release of bacteria or aggregates, possibly from skin shedding.
- Particle size monitoring is a valuable tool for understanding indoor bacterial dynamics.
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