Caren B. Les, email@example.com
ALBUQUERQUE, N.M. – Polymer surfaces working in tandem with fluorescent lighting could reduce
the spread of dangerous bacteria in hospitals and other clinical settings. Hospital
staff could simply turn on regular fluorescent lighting to activate the antimicrobial
properties of such surfaces, reducing the need for more labor-intensive methods
of disinfection. And scientists have now taken a step forward in developing this
light/polymer combination technique.
The Centers for Disease Control and Prevention in Atlanta estimates
1.7 million hospital-associated infections and 99,000 associated deaths each year
in the US from bacteria such as methicillin-resistant Staphylococcus aureus (MRSA)
and, particularly, Gram-negative bacteria, which tend to be harder to kill than
Researchers are experimenting with
surfaces that may kill harmful bacteria in hospitals with the help of fluorescent
lighting. The colorized scanning electron micrograph depicts clumps of the MRSA
bacteria, magnified 2390x. Courtesy of the Centers for Disease Control and Prevention.
David G. Whitten at the Center for Biomedical Engineering at the
University of New Mexico in Albuquerque and Kirk S. Schanze at the University of
Florida in Gainesville have developed a number of conjugated polyelectrolytes (CPEs)
that have potential as biocides toward bacteria, said Heather E. Canavan, assistant
professor in the department of chemical and nuclear engineering at the University
of New Mexico and at the Center for Biomedical Engineering.
They have shown that while certain polymers demonstrate biocidal
activity toward certain bacteria, they do not appear to be toxic to mammalian cells
that have been exposed to polymers in both light and dark conditions. Results of
their study, which is at the in vitro stage, have indicated that the technique may
be safe for humans and animals.
Specifically, the researchers first demonstrated that certain
CPEs with arylene ethynylene repeat-unit structure exhibit dark- and light-activated
antimicrobial activity. For example, certain light- activated CPEs exhibit little
activity toward bacteria in the absence of light but display significantly greater
bacteria-killing activity with the addition of light. In experiments, the polymer/lighting
combination has been effective at killing Gram-negative bacteria, specifically the
Pseudomonas aeruginosa strain PAO1 and Cobetia marina.
The researchers are now experimenting to determine whether the
CPEs, in amounts needed for disinfection applications, would be toxic to humans
and animals. “We’re finding that mammalian cells such as bovine aortic
endothelial cells are capable of tolerating those polymers at much higher doses
(an order of magnitude or more),” Canavan said. “It’s the first
step to developing commercial applications from these materials.”
One of the first challenges that must be overcome is ensuring
that, while the CPEs are suitably toxic to prokaryotic cells (bacteria), they are
nontoxic to mammalian cells, especially human cells, when they come into normal
contact with them. “If we can demonstrate that, then the next step would be
to perform simple initial in vivo tests,” Canavan said.
In the experiment, the researchers cultured mammalian cells, specifically
bovine aortic endothelial cells, on 48-well plates. They replaced the cells’
regular growth medium with a serum-free medium that had been treated with the CPE
at concentrations varying from 1 to 100 µg/ml. The cell culture plates, loosely
covered in foil, were returned to the incubator for 24 hours. Then the cells were
washed with Dulbecco’s phosphate-buffered saline, and the cells in the negative
control wells were treated with a 70 percent (vol.) methanol solution for 30 min.
To assess cytotoxicity, the researchers used a live/dead fluorescence assay and
obtained images on an inverted microscope with an epifluorescence attachment.
The underlying mechanism of how the CPE material kills bacteria
is still under investigation, Canavan said. The researchers see differences in
the extent and efficiency of killing of various CPEs in light and dark situations,
which may indicate that the light activation includes release of reactive oxygen
species such as singlet oxygen.
“There are many applications where a material may come into
contact with both eukaryotic (mammalian, plant) and prokaryotic (bacteria) cells,
and you’d want to minimize the transfer of bacteria to mammalian cells,”
Canavan said. “For instance, in addition to the fixed surfaces in hospitals,
there are a lot of consumable materials, such as catheters and wound dressings that
come into direct contact with patients. All of these carry the potential to transfer
bacteria to the patient, resulting in health care-associated infection.”
The overall interdisciplinary project involves students and faculty
in different locations and research groups working together to develop new polymers,
test their biocidal activity toward bacteria, test their biocompatibility with mammalian
cells, and model how the polymers interact with cells.