# The combined 410nm and infrared light effectively suppresses bacterial survival under realistic conditions

## TL;DR

Combining 410nm violet and infrared light effectively kills drug-resistant bacteria in realistic settings.

## Contribution

Demonstrates that 410nm violet light with infrared is a practical and inexpensive method for suppressing bacterial survival.

## Key findings

- Combined 20W 410nm and 850nm infrared light suppressed over 91-97% of E. coli and 96-99% of S. aureus at short distances within 1–6 hours.
- Bacterial suppression decreased with distance, requiring longer exposure times at 1m or 2m.
- Mechanistic studies showed increased ROS levels and reduced biofilm thickness as causes of bacterial death.

## Abstract

The demand for establishing an effective but inexpensive method to interfere with the spread of infectious diseases has been higher than ever before, since the recent pandemic. As a follow-up study, we tested a few practically applicable lights with a safe 410nm violet light (V) with infrared (IR, 850nm) under realistic conditions to identify an optimal light for suppressing pathogens. Our results indicate that 410nm violet light is as effective as the previously tested 405nm violet light with infrared (850nm). Therefore, we focused on optimizing combined lights (3V-1IR or 2.33V-1IR) with lower power level that is below 24 Watt. Using the Multi Drug Resistant (MDR) Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) from ATCC, we confirmed that the combined 20W light effectively suppressed the survival of both MDR bacterial strains on a smooth surface at the distance of 25cm, 50cm, 1m or 2m, which mimicked the realistic living spaces. As expected, the effectiveness was inversely proportional to the exposed distance. For example, the light exposure suppressed more than 91-97% of E. coli within 1–2 hours and 96-99% of S. aureus within 2–6 hours at short distances (25 or 50cm), whereas it took 6–8 hours to reach 92-95% of E. coli and 91-99% of S. aureus suppression at 1 or 2m. In the mechanistic studies, we confirmed that the bacterial death was mediated by the enhanced level of Reactive Oxygen Species (ROS), in addition to reduced thickness of biofilm from 410nm and 850nm infrared light. Our results strongly support the possible application of using this combined 410nm with infrared light as an inexpensive and practical solution to reduce the potential pathogens, at least from bacterial origins in a variety of living spaces.

Created by Dinesh K Verma in BioRender. Kim, YH. (2025) https://BioRender.com/e50i242

Diagram illustrating a laboratory procedure to test the effect of different lighting conditions and durations on bacterial growth. Step 1 shows petri dishes placed at varying distances (25 cm, 50 cm, 1 m, 2 m) under two lighting conditions: no light/white light and 10W/20W/24W light at 410 nm/850 nm for different durations (1.5 h, 3 h, 6 h, 12 h). Step 2 involves re-suspending the bacteria solution in 500 µl PBS. Step 3 shows pipetting E. coli or S. aureus onto agar plates. Step 4 involves spreading the sample and incubating at 37°C overnight. Step 5 displays results of bacterial growth under different conditions.