TROY, NY - Building on an enzyme found in nature, researchers at Rensselaer Polytechnic Institute have created a nanoscale coating for surgical equipment, hospital walls and other surfaces that safely eradicates methicillin-resistant Staphylococcus aureus (MRSA), the bacteria responsible for antibiotic-resistant infections.
“We’re building on
nature,” said Jonathan S. Dordick, the Howard P. Isermann Professor of Chemical
and Biological Engineering, and Director of Rensselaer’s Center for
Biotechnology & Interdisciplinary Studies. “Here we have a system where the
surface contains an enzyme that is safe to handle, doesn’t appear to lead to
resistance, doesn’t leach into the environment and doesn’t clog up with cell
debris. The MRSA bacteria come in contact with the surface, and they’re
In tests, 100 percent of
MRSA in solution were killed within 20 minutes of contact with a surface
painted with latex paint laced with the coating.
The new coating marries
carbon nanotubes with lysostaphin, a naturally occurring enzyme used by
non-pathogenic strains of Staph bacteria to defend against Staphylococcus
aureus, including MRSA. The resulting nanotube-enzyme “conjugate” can be mixed
with any number of surface finishes; in tests, it was mixed with ordinary latex
Unlike other antimicrobial
coatings, it is toxic only to MRSA, does not rely on antibiotics, and does not
leach chemicals into the environment or become clogged over time. It can be
washed repeatedly without losing effectiveness and has a dry storage shelf life
of up to six months.
The research, led by
Dordick and Ravi Kane, a professor in the Department of Chemical and Biological
Engineering at Rensselaer, along with collaboration from Dennis W. Metzger at Albany Medical
College, and Ravi
Pangule, a chemical engineering graduate student on the project, has been
published in the July edition of the journal ACS Nano, published by the
American Chemical Society.
Dordick said the
nanotube-enzyme coating builds on several years of previous work embedding enzymes
into polymers. In previous studies, Dordick and Kane discovered that enzymes
attached to carbon nanotubes were more stable and more densely packed when
embedded into polymers than enzymes alone.
“If we put an enzyme
directly in a coating (such as paint) it will slowly pop out,” Kane said. “We
wanted to create a stabilizing environment, and the nanotubes allow us to do
Having established the
basics of embedding enzymes into polymers, they turned their attention to
“We asked ourselves -
were there examples in nature where enzymes can be exploited that have activity
against bacteria?” Dordick said. The answer was yes and the team quickly focused on lysostaphin,
an enzyme secreted by non-pathogenic Staph strains, harmless to humans and
other organisms, capable of killing Staphylococcus aureus, including MRSA, and
“It’s very effective. If
you put a tiny amount of lysostaphin in a solution with Staphylococcus aureus,
you’ll see the bacteria die almost immediately,” Kane said.
Lysostaphin works by
first attaching itself to the bacterial cell wall and then slicing open the
cell wall (the enzyme’s name derives from the Greek “lysis” meaning “to loosen
or release”). “Lysostaphin is
exceptionally selective,” Dordick said. “It doesn’t work against other
bacteria, and it is not toxic to human cells.”
The enzyme is attached to
the carbon nanotube with a short flexible polymer link, which improves its
ability to reach the MRSA bacteria, said Kane. “The more the lysostaphin
is able to move around, the more it is able to function.” Dordick said.
They successfully tested
the resulting nanotube-enzyme conjugate at Albany Medical
College, where Metzger
maintains strains of MRSA.
“At the end of the day,
we have a very selective agent that can be used in a wide range of environments
- paints, coating, medical instruments, door knobs, surgical masks - and it’s
active and it’s stable,” Kane said. “It’s ready to use when you’re ready to use
approach is likely to prove superior to previous attempts at antimicrobial
agents, which fall into two categories: coatings that release biocides or
coatings that “spear” bacteria.
Coatings that release
biocides, which work in a manner similar to marine anti-fouling paint, pose
harmful side effects and lose effectiveness over time as their active
ingredient leaches into the environment.
Coatings that spear
bacteria, using amphipatic polycations and antimicrobial peptides, tend to
clog, also losing effectiveness.
The nanotube-lysostaphin coating does
neither, said Dordick.
“We spent quite a bit of
time demonstrating that the enzyme did not come out of the paint during the
antibacterial experiments. Indeed, it was surprising that the enzyme worked as
well as it did while remaining embedded near the surface of the paint,” Dordick
The enzyme’s slicing or
“lytic” action also means that bacterial cell contents disperse, or can be
removed by rinsing or washing the surface. Kane also said MRSA are
unlikely to develop resistance to a naturally occurring enzyme.
“Lysostaphin has evolved
over hundreds of millions of years to be very difficult for Staphylococcus
aureus to resist,” Kane said. “It’s an interesting mechanism that these enzymes
use that we take advantage of.”
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