UBC Okanagan Assistant Professor Sepideh Pakpour, along with student researchers Enrique Calderon and Rita Lam, examine a sample beside the natural light experimentation chamber. Their research suggests light through smart windows can work as a natural disinfectant against many illnesses, including E.Coli and methicillin-resistance Staphylococcus aureus. Credit: UBC
Never in recent history has the ventilation, cleaning and filtration of air inside buildings been of more concern than the ongoing COVID-19 pandemic. But, a team of researchers from the University of British Columbia (UBC) says we’re ignoring a critical solution: daylight.
“We know daylight kills bacteria and fungi. But the question is, are there ways to harness that benefit in buildings, while still protecting us from glare and UV radiation?,” says Sepideh Pakpour, assistant professor at UBC Okanagan’s School of Engineering, and author of a recent study on the topic.
In their research, Pakpour and her team tested four strains of bacteria—methicillin-resistance Staphylococcus aureus (MRSA), Klebsiella pneumoniae, E. coli and Pseudomonas aeruginosa—and fungi using a mini-living lab setup outfitted with smart windows, which tint dynamically based on outdoor conditions.
The tested microbes were placed on polyvinyl chloride (PVC) fabric, polystyrene and glass for 24 hours (bacteria) and 72 hours (fungi) to evaluate the effect of indoor daylight through the smart windows.
Results showed that gram-positive bacteria, like MRSA, were more susceptible to indoor daylight than gram-negative bacteria, such as E.coli. For example, clear windows reduced the viability of MRSA by 96% on polystyrene surfaces and 100% on glass. Tinted windows also reduced MRSA by 100% on PVC fabric. And while E.coli’s growth rate was significantly reduced by both clear and tinted windows on PVC fabric, only tinted windows managed to slow the gram-negative bacteria down when on glass. No growth reduction was observed when E.coli was on polystyrene.
The researchers attribute this difference to the higher blue light susceptibility of gram-positive bacteria, but say further investigations on the topic are needed as previous literature offers contradictory findings.
Three of the tested bacterial strains—MRSA, K. pneumoniae and P. aeruginosa—are represented in ESKAPE, the acronym comprising the scientific names of six highly virulent antibiotic-resistant pathogens that correspond with the highest risk of mortality.
“This highlights the importance of our results as disinfections of antibiotic resistant pathogens are becoming increasingly challenging, considering nearly every current antibiotics have been observed with microbial resistance,” the authors write in the study, which has been published ahead of peer-review in bioRxiv.
On the fungal side, pathogens were mostly reduced when hit with sunlight through a clear window, especially when on polystyrene surfaces. For example, both A. fumigatus and A. versicolor demonstrated a 55% reduction in these conditions. Tinted windows also reduced the viability of the two fungal pathogens but to a lesser degree—23 to 27%. The same held true for S. chartarum on PVC fabric—growth reduction of 60% through a clear window, and only 39% through a tinted window.
According to the study authors, the fungal pathogens were more affected by light intensities than spectrum, hence the light effect was mostly seen with clear windows. This is in contrast to the bacterial pathogens, which reacted more to the high energy blue light spectrum at wavelength of 400-500 nm transmitted through the tinted windows.
In fact, blue light therapy has been shown to be effective against a wide range of microorganisms, a fact researchers say could be a promising intervention for disease controls in the future.
“[This] window technology shows promising potential to replace blinds as the predominant glare control strategy, which previous studies have shown to improve cognitive function and psychological health of the occupants,” the research team concludes. “This study also further expands its potential in minimizing disease transmission, which could be implemented in various built environments for shaping healthy indoor microbiomes toward the occupants.”