Bacteria killed by light-activated coating

To stop the spread of disease, it could be used to coat phone screens and keyboards, as well as the inside of catheters and breathing tubes, which are a major source of healthcare-associated infections (HCAIs).

The most well-known HCAIs are caused by Clostridioides difficile (C. difficile), methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli). They commonly occur during in-patient medical or surgical treatment, or from visiting a healthcare setting and pose a serious health threat.

The research is the first to show a light activated antimicrobial coating successfully killing bacteria in low intensity, ambient light (300 Lux), such as that found in wards and waiting rooms. Previously, similar coatings needed intense light (3,000 Lux), like that found in operating theatres, to activate their killing properties.

The new bactericidal coating is made of tiny clusters of chemically modified gold embedded in a polymer with crystal violet -- a dye with antibacterial and antifungal properties.

First author, Dr Gi Byoung Hwang (UCL Chemistry), said: "Dyes such as crystal violet are promising candidates for killing bacteria and keeping surfaces sterile as they are widely used to disinfect wounds. When exposed to bright light, they create reactive oxygen species, which in turn kill bacteria by damaging their protective membranes and DNA. This is amplified when they are paired with metals such as silver, gold and zinc oxide."

The team of chemists, chemical engineers and microbiologists created the bactericidal coating using a scalable method and tested how well it killed S. aureus and E. coli against control coatings and under different lighting conditions.

Sample surfaces were treated with either the bactericidal coating or a control coating before being inoculated with 100,000 colony forming units (CFU) per ml of either S. aureus and E. coli. The growth of the bacteria was investigated under dark and white light conditions between 200 -- 429 Lux.

They found that in ambient light, a control coating of crystal violet in a polymer alone did not kill either bacteria. However, in the same lighting conditions, the bactericidal coating led to a 3.3 log reduction in the growth of S. aureus after six hours and a 2.8 log reduction in the growth of E. coli after 24 hours.

See:

Gi Byoung Hwang, He Huang, Gaowei Wu, Juhun Shin, Andreas Kafizas, Kersti Karu, Hendrik Du Toit, Abdullah M. Alotaibi, Layla Mohammad-Hadi, Elaine Allan, Alexander J. MacRobert, Asterios Gavriilidis, Ivan P. Parkin. Photobactericidal activity activated by thiolated gold nanoclusters at low flux levels of white light. Nature Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-15004-6

Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (http://www.pharmamicroresources.com/)