A handy way to stop an infection is to fill a germ's pocket with gold. Scientists have failed to translate this knowledge into an effective antimicrobial treatment.
Researchers from the UK's University of Leeds and China's Southern University of Science and Technology joined forces recently to repackage nanoclusters of gold to make them more attractive to bacteria and less harmful to our bodies.
The team created a particle by weaving together the gold and two molecules with different levels of electrostatic stickiness. This particle can be used to attack many common bacterial pathogens, but it will not cause any harm to surrounding tissues.
Gold might not appear to be an obvious treatment for germ killing at first glance. This heavyweight element, which is reduced to a fine dust on a nanoscale, can cause serious damage.
This is possible because gold nanoparticles facilitate chemical reactions that can release oxygen species capable to damaging DNA. Another way is to alter cell membranes and make them more susceptible to toxic substances like antibiotics. They can also absorb laser light with high efficiency, heating up their surroundings and roasting them.
These handy methods of treating infections can't always distinguish between host and bacteria, which puts our cells at risk due to gold nanoparticle therapies.
It is necessary to find a way to encourage bacteria and keep our cells from grabbing as much gold as possible.
Engineers have modified the behavior of gold nanoparticles two times in recent years.
One is to control their size. The particles should not exceed two nanometers in size. This allows them to pass through our kidneys more easily and makes it easier for them to leave our bodies faster. Researchers focused their efforts on limiting their clusters to 25 atoms.
The second involves incorporating ligands (sticky chemical structures), which allow for the incorporation of various features that can be tracked and controlled to control the particle's form.
The team applied a positively charged compound to the clusters in this instance, hoping that the negatively charged bacterial cells would attract gold the same way a sweater attracts cat fur.
To make gold therapy more clinically feasible, it would be worth tweaking the particles to make them less likely to cause harm to the host. However, previous studies have not been able to cap gold nanoparticles using more than one type of ligand. This is because different methods of integrating ligands are often incompatible.
The winning formula was based on a positive-charged compound called Pyridium and a zwitterion (a compound that has both positively and negative charged groups).
The pyridinium makes the gold more attractive for bacteria. Based on previous studies, the zwitterion was selected because it demonstrated improved stability and greater compatibility with animal tissues.
The augmented gold nanoclusters were tested on methicillin-resistant Staphylococcus epidermidis. It also produced reactive oxygen species and damaged the integrity of its membranes.
Even better, the number of bacterium cells dropped when they were treated with antibiotics. One case showed that the MRSE was inhibited by a lower dose than usual. This resulted in a decrease of more than 100 percent.
The gold nanoparticles helped heal skin infections in rats with MRSE.
Dejian Zhou from Leeds, a chemical engineer, says that by systematically tuning the ratios of the two ligands we have found a way to use gold nanoclusters as effective antimicrobial agents as well as as a mechanism for increasing the potency antibiotics that have become ineffective due to bacterial drug resistance.
"The research has an important significance for the way we should think about responding to antimicrobial resistant."
The growing resistance to antibiotics is a major problem in modern medicine. It threatens to render some of our most valuable defenses against infection unusable.
It is great to find new ways of killing bacteria. It would be a relief to find ways to preserve our existing treatments.
This could be a chance to protect ourselves from the same diseases that have claimed so many lives over time.
This research was published by Chemical Science.