Objective

Characterize the efficacy of the Defend 1050 against three aerolized microorganisms: Enterobacter cloacae, a gram-negative bacterium; Salmonella enterica, a gram-negative bacterium; Listeria innocua, a gram-positive bacterium. 

This study characterized the Defend 1050 air purifier's efficacy in removing three species of respirable bioaerosols using a sealed 16m³ testing chamber. Two methods were used: 1) the single-pass efficiency was tested to calculate the CADR, and 2) chamber trials were performed to prove the device's efficacy in an indoor environment.

The species tested were Enterobacter cloacae, a gram-negative bacterium; Salmonella enterica, a gram-negative bacterium; and Listeria innocua, a gram-positive bacterium. These are typical food and airborne pathogens that can be found in public places and cause various illnesses. Consequently, the United States Department of Agriculture (USDA) and the Food and Drug Administration (FDA) are concerned with controlling their spread.

Methodology

Each microorganism was aerosolized into a sealed 16m³ environmental bioaerosol test chamber containing the test device using a Collison 24-jet nebulizer. For the single-pass testing, sampling was performed by simultaneously capturing bioaerosols directly at the inlet and outlet of the device and calculating the percent reduction.

Three trials were performed for each organism and the results averaged. For the chamber trials, twelve (12) live bioaerosol trials were performed; three species each were tested in triplicate, including one control trial per organism. Bioaerosol samples were then taken from the chamber at multiple time points throughout each trial to quantify the reduction rate of the recirculating air cleaner.

Chamber control trial data, or natural decay, was subtracted from the device trial data to yield the net log reduction for each bioaerosol challenge. All samples were serially diluted, plated, incubated, and enumerated in triplicate to yield viable bioaerosol concentrations before and after passing through the device.

Summary of Results

The average single-pass reduction measured was 3.97 ± 0.03 log, or 99.989%, resulting in a CADR of 533 cfm. In chamber trial tests, the device effectively reduced all three bioaerosol challenge organisms by a net log of 4.0 or greater (equivalent to 99.99% or greater) within 15 minutes, exceeding a 6 net log reduction in 20 minutes.

Conclusion

The device quickly reduced three species of airborne microorganisms in the chamber trials. This is due to the device's high efficiency, which resulted in a 533 cfm CADR.