Evaluation of Microbial Survival and DNA persistence in HVAC Filters

Abstract

Background: Heating, ventilation and air conditioning (HVAC) filters remove both particulate matter and microorganisms from indoor environments. They thus can improve indoor air quality and also serve as a microbial reservoir for forensic studies. Recovering and analyzing the microbial community trapped within HVAC filter dust is a useful approach for delineating the indoor microbiome present in a wide variety of buildings including residential homes, commercial buildings and even retail stores. Aims: The objective of this study was to evaluate DNA recovery from HVAC filter dust under simulated HVAC operating conditions. Methods: HVAC filters with sterilized HVAC dust were spiked with known concentrations of Aspergillus niger and Bacillus cereus. The loaded HVAC filter dust was then subjected to air flow and relative humidity conditions typical of HVAC operation. DNA was extracted on days 0, 1, 4, 7, and 17 and cell counts were estimated via qPCR. Results: The results indicate that the specific filter dust type has an impact on DNA extraction efficiency, with 60% of the initially loaded cells recovered immediately following spiking from one filter and fewer than 20% recovered from the other. Generally, the DNA was recoverable within 7 days of inoculation even under the simulated airflow conditions. After 17 days of airflow, less than 5% of the spiked DNA was recoverable from the filter dust. Conclusions: The results of this study are important in applying HVAC filters as indoor microbial samplers for future investigations. The results suggest that filter dust inhibits DNA amplification to varying levels, suggesting that positive controls should be utilized to determine sample extraction efficiency. The data indicate that the DNA from the model organisms was recoverable after exposure to airflow for 7 days with minimal loss. However, additional exposure past seven days resulted in a considerable reduction in the DNA recovered.