Silence the bacteria

Bacteria prefer wet surfaces
.
Once they settle there, they no longer live alone, but form larger groups, embedded in a
protective film.
These biofilms are found on a variety of surfaces, such as on light switches at home, in the bathroom, on toys or keyboards, in shopping carts or ATMs that many people touch with their hands
.
This can lead to contact infection
.
These bacteria, such as the pathogenic bacterium Pseudomonas aeruginosa, are usually persistent and unaffected by
the body's own immune system or chemical biocides.
Therefore, the current research method is to try to prevent bacteria from colonizing the surface of the material, or at least increase the difficulty
of colonization.
A team from Johannes Gutenberg University Mainz (JGU) and the German Federal Institute of Hydrology (BfG) in Koblenz has now developed a new method
using cerium dioxide nanoparticles.

Modified signaling molecules prevent biofilm formation

For bacterial life in a community, it is important
for individual cells to "talk" to each other.
With the help of signaling molecules constantly released into the environment, bacteria communicate nonverbally, so different "languages" and "dialects" can be produced
according to specific bacteria.
As the concentration of bacteria increases, so does the concentration of signaling molecules
.
This allows the bacteria to detect the number of other bacteria in the environment and activate the process of
forming biofilms.

To prevent colonization of bacterial biofilms, various hosts protect themselves
through the strategy of "silencing" bacteria through enzyme-modifying signaling molecules.
This is done, for example, with the help of haoperoxidases, a group of enzymes
that halogen signal molecules through complex reaction chains.

These modified signaling molecules have a similar structure to the original molecule and can still bind
to the acceptor.
However, they can no longer activate the chain
of processes that lead to biofilm formation.
This interference with bacterial gene regulation also has pharmacological implications, as pathogenic bacteria can form biofilms to avoid attacks from epidemic defenses or the action of
antibiotics.

Cerium dioxide nanoparticles replace the function of natural enzymes

Researchers at Mainz and Koblenz simulated these processes
with cerium dioxide nanoparticles (CeO2).
As the researchers explain in a recent paper published in ACS Nano, CeO2 nanoparticles are a functional alternative to
salt peroxidase.
However, the molecular mechanisms of biofilm inhibition are difficult to elucidate in detail because not only do many competitive reactions occur in bacterial culture, but a large number of other biomolecules
are present in addition to halogenated signaling molecules.

The partners of Mainz and Koblenz demonstrated the enzymatic-analogue catalytic involvement
of CeO2 nanoparticles by analyzing the reaction cascade at the molecular level.
Halogenated signaling molecules were first discovered in model reactions
.
In bacterial culture, products degrade too quickly to detect them
directly.
However, chromatography and mass spectrometry unexpectedly revealed the formation
of further halogenated signaling molecules from the so-called quinolone family.
This suggests that CeO2 nanoparticles interfere with biological processes by modifying and inactivating signaling molecules, just like native enzymes
.

Antimicrobial surfaces are made possible without the risk of developing resistance

"Cerium dioxide is non-toxic and chemically stable, for example, it is found in modern automobile exhaust catalytic converters," says Dr.
Eva Pütz, whose doctoral thesis was about the project
.
She is convinced that cerium dioxide is a viable, cost-effective alternative to
traditional biocides in general.
"One practical application we found is to stop bacterial growth and prevent bacterial infection," she said
.
Quinolone signaling molecules lead to the formation of small colony variants in multidrug-resistant Staphylococcus aureus, which is often undiagnosed
.
Since the haloquinolone signaling molecule inhibits colony formation, for example, dangerous infections of Pseudomonas aeruginosa and Staphylococcus aureus can be prevented with the help of coating dispersions containing CeO2 nanoparticles," adds Dr.
Athanasios Gazanis, who studied the microbiological aspects in
his doctoral thesis.

"Here we have an environmentally compatible component for a new generation of antimicrobial surfaces that mimic nature's defense systems
.
Above all, it is effective not only in the laboratory, but also in everyday use," emphasizes Nils Keltsch, who carried out biomicroanalysis
in his doctoral thesis.

The danger of fighting biofilms with fungicides and antibiotics lies in the formation
of drug resistance.
However, by coating CeO2 nanoparticles on polymers, this problem
can be effectively circumvented in an environmentally friendly way.