In
the presence of nanoparticles, the cell wall of the bacteria ends up breaking
seemingly by stretching, like a balloon that is inflated from different points
until it exploded. Courtesy: Universitat Rovira i Virgili.
Finding
alternatives to antibiotics is one of the biggest challenges facing the
research community. Bacteria are increasingly resistant to these drugs, and
this resistance leads to the deaths of more than 25,000 around the world. Now,
a multidisciplinary team of researchers from the Universitat Rovira i Virgili,
the University of Grenoble (France), the University of Saarland (Germany) and
RMIT University (Australia) have discovered that the mechanical deformation of
bacteria is a toxic mechanism that can kill bacteria with gold nanoparticles.
The results of this research have been published in the journal Advanced Materials
and are a breakthrough in researchers' understanding the antibacterial effects
of nanoparticles and their efforts to find new materials with bactericide
properties.
Since the
times of Ancient Egypt, gold has been used in a range of medical applications
and, more recently, as for diagnosing and treating diseases such as cancer.
This is due to the fact that gold is a chemically inert material, that is, it
does not react or change when it comes into contact with an organism. Amongst
the scientific community, nanoparticles are known for their ability to make
tumors visible and for their applications in nanomedicine.
This new
research shows that these chemically inert nanoparticles can kill bacteria
thanks to a physical mechanism that deforms the cell wall. To demonstrate this,
the researchers have synthesized in the laboratory gold nanoparticles in the
shape of an almost perfect sphere and others in the shape of stars, all
measuring 100 nanometres (8 times thinner than a hair). The group analyzed how
these particle interact with living bacteria. "We find that the bacteria
become deformed and deflate like a ball that is having the air let out before
dying in the presence of these nanoparticles," explained Vladimir Baulin,
researcher at the Department of Chemical Engineering of the URV. The
researchers state the bacteria seem to have died after a massive leak, "as
if the cell wall had spontaneously exploded."
The
scientists thought that a physical mechanism might be responsible for the death
of the bacteria. Consequently, they carried out aa numerical simulations to
analyze how a homogenous layer of individual nanoparticles could apply
sufficient mechanical tension to the cell wall of the bacteria that it ends up
breaking seemingly by stretching, like a balloon that is inflated from
different points until it exploded.
To confirm
this hypothesis, the researchers created an artificial model of a bacterial
cell membrane to evaluate its response when it entered into contact with the
100 nm gold nanoparticles. "We found that the model spontaneously
contracted until it completely collapsed, thus proving the hypothesis that
nanoparticles apply a mechanical stretch on the cell membrane of the
bacteria," Baulin asserted.