Viable airborne microbial counts are commonly used in indoor air quality (IAQ) assessment, but studies linking the microbial counts to a specific type of indoor microbial contamination are limited. We hypothesize that the airborne microbial counts can differentiate air-cooling units with and without complaints of urine and body odors. The keratinolytic property of some isolated bacteria prompts to the hypothesis that keratinase is present in the units to break down keratins, structural proteins that form human skin scales, as sources of amino acids and ammonium to produce the odors. Seven bacterial species and four fungal species were identified in the units and room air. Airborne Staphylococcus haemolyticus and Methylobacterium organophilum counts contributed the most to the microbial dissimilarities of units with and without odor complaints. Keratinolytic bacteria and a methylotrophic bacterium were abundant in the units. All the units contained ammonium, and keratinase activity was higher in the units with odor complaints. Extracellular keratinase activity was more effective at 20 °C than at 30 or 4 °C. Keratinolytic bacteria produced high levels of ammonium in the culture with skin cells. Viable airborne microbial counts can help IAQ inspectors to identify potential odor-causing air-cooling units. Keratins may be broken down in the units and associated with the odor complaints.
Bibliographical noteWe thank the HKBU Estate Office and Health and Safety team for assisting the field investigation and the Environment and Conservation Fund (Grant Ref.: ECF89/2015) for supporting this study.
- Air-conditioning systems
- Indoor air quality
- Microbial odor emission