Dual frequency illumination fights E. coli superbugs

01 Aug 2023

New Zealand's AgResearch combines blue and UV light to counter antibiotic resistance.

The ability of bacteria and microbial pathogens to become resistant to the antimicrobial treatments intended to kill them is a global issue, identified by the World Health Organisation (WHO) as one of the top ten health concerns.

Optical techniques have been valuable tools in the fight against antimicrobial resistance (AMR), stemming principally from the ability of UV light and ultrashort-pulse illumination to disrupt the protein structures in a pathogen and alter its potency.

Use of basic UV irradiation is not a perfect solution, however. Beyond the potential for damage to healthy cells, there are many mechanisms through which bacteria can adapt to UV exposure and repair the protein damage caused by the light. Repetitive exposure can also breed tolerance and an increase in AMR.

A project at New Zealand research institute AgResearch has now studied a novel dual wavelength regime, whereby bacteria are illuminated with both blue and far-UVC light.

The group targeted extended spectrum β-lactamase producing E. coli (ESBL-Ec), a treatment-resistant bacteria listed as a Priority 1 pathogen by the WHO.

"Our previous work showed that dual blue LED and far-UVC wavelengths were virucidal against feline infectious peritonitis virus (FIPV) in solution and on different surfaces, indicating the potential of dual light wavelengths to be effective against bacteria," commented the project in its Journal of Applied Microbiology paper.

"In this study, we aimed to investigate the effect of dual blue LED (405 nanometer) and far-UVC (222 nanometer) light on the inactivation of clinically relevant ESBL-Ec, and determine whether repetitive exposure to long pulse doses of dual or individual light wavelengths results in changes to light tolerance and antibiotic susceptibility."

Disinfection of public places in shorter times

In trials, the AgResearch group found that combining the two wavelengths inhibited the potency of the E. coli, by triggering different mechanisms that disrupt the activity of the microorganisms. The same method was also shown to deactivate another variant of E. coli that does respond to antibiotic treatment, suggesting that the dual-light technique could be used to combat a broad range of harmful microbes.

The overall effect achieved by a dual light treatment was always greater than that from exposure to the wavelengths individually, indicating a synergistic relationship between blue LED and far-UVC light when used together.

However, the researchers also found that ESBL-Ec can start to tolerate light after repeated irradiation at sublethal levels, an effect that was not observed for the variant that is sensitive to antibiotics. So further work is needed to understand whether the light tolerance exhibited by ESBL-Ec might be caused by a genetic change or whether some other mechanism is involved, according to the AgResearch team.

If dual light illumination can be optimized, it may allow whole-room disinfection in shorter timescales than those needed for current UV-only methods, as lower far-UVC doses would be expected to achieve the same outcome. But for that to happen, the safety of dual far-UVC and blue LED light applications in public places would need to be investigated, noted the project.

"There is great potential for these two light wavelengths to be used together in many applications where safety to the end user is of most importance," commented Amanda Gardner of AgResearch. "It will also be important to investigate the development of light tolerance in other antimicrobial-resistant bacteria, and to determine the minimum dose of far-UVC light that can create light tolerance."