AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Influence of Relative Humidity on Indoor Bacterial and Fungal Communities
KAREN C. DANNEMILLER, Charles Weschler, Jordan Peccia, Yale University
Abstract Number: 492 Working Group: Indoor Aerosols
Abstract Carpeted floors are a major source of bacteria and fungi suspended in indoor air. The origin of microbes in carpeting is known to include tracked-in and settled dust and growth in water damaged areas, but it is unclear if bacterial and fungal growth occurs indoors under normal building conditions where humidity levels fluctuate with time. We hypothesize that water absorbs from the air, providing sufficient moisture for microbial growth in carpets. An experimental chamber study was conducted on carpet samples loaded with house dust to measure microbial growth under controlled relative humidity conditions varying from 50%-100%. Total fungal and bacterial concentrations were measured by quantitative polymerase chain reaction (qPCR), and we explored microbial community changes associated with increased indoor moisture using DNA sequencing of the16S (bacteria) and ITS (fungi) regions. In chamber experiments, the moisture content of the carpet samples stabilized within 24 hours. Based on one week growth experiments, fungal growth was observed at ≥80% relative humidity, and bacterial growth was observed only at 100% relative humidity. During this initial week, the 100% relative humidity conditions resulted in 27 times increase in fungal concentration and 2.7 times increase in bacterial concentration compared to the starting concentrations. About half (44-51%) of fungal growth occurred within the first week after a change in relative humidity. Fungal growth rates after the initial week were 8,500 (±3,050) spore equivalents•day$_(-1)•mg dust$_(-1) at 85% relative humidity and 113,000 (±13,700) spore equivalents•day$_(-1)•mg dust$_(-1) at 100% relative humidity. Microbial communities changed under conditions when growth occurred. While previous studies have assumed that bacterial and fungal growth does not contribute to microbial communities in carpets in building without overt moisture damage, we demonstrate that growth significantly impacts these communities at ≥80% relative humidity.