INSTEAD of giving people antibiotics, doctors may soon give them a dose of
genetically engineered superviruses instead. Researchers have turned the natural
viruses that infect bacteria into much more efficient killers. Such viruses, or
bacteriophages, are harmless to humans. They only attack specific bacteria, into
which they inject their genetic material, forcing the cells to make more
viruses. Eventually, the infected cells burst open, releasing all the new
viruses.
Since the 1920s, phages have been used to treat infections in people, animals
and even plants. But the technique has never really caught on. One problem is
that the natural viruses have evolved to replicate themselves, rather than to
kill cells. So researchers in the US have adapted a technique usually used in
gene therapy鈥攖o introduce genes into human cells鈥攖o deliver a lethal
message to disease-causing bugs.
The technique could treat deadly antibiotic-resistant infections in people
with severe burns, cystic fibrosis or other diseases.
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The South Carolina team has found a way to trick the phage into injecting
altered DNA into bacteria. The DNA codes for a protein that will tell the
bacteria to commit suicide. 鈥淭he bacteria end up making the protein that鈥檚 going
to kill them,鈥� says study co-leader David Schofield from the Medical College of
South Carolina in Charleston.
The researchers chose the virus P1, which latches onto a variety of bacterial
strains. To turn it into a lethal weapon, the team added engineered DNA to a
solution of bacteria already infected with normal P1. The engineered material
not only makes the suicide protein, it also has all the tags the phage looks for
before packaging up its own DNA into new virus particles.
The engineered DNA is taken up by bacterial cells, where it is packaged into
millions of new phage particles. 鈥淚t鈥檚 like a company manufacturing it,鈥� says
Caroline Westwater, a member of the South Carolina team. They filter the
solution to isolate the phage for injection.
Currently, the filtered solution contains both redesigned and normal phage
particles, as the group is not yet able to force the phage to preferentially
package the re-engineered DNA. But the group is working on ways to make that
happen. Removing the recognition sites on the viruses鈥� own DNA might do the
trick, they say.
When researchers tested their virus on mice with infected burns covering 20
per cent of their body, applying phage solution to the burns dramatically
increased the survival of the mice. If all goes well, they hope to begin human
trials within two years.
鈥淚t does have some potential,鈥� says Ian Molineux, a microbiologist at the
University of Texas in Austin, who is trying to get unaltered phages to destroy
bacteria.
Todd Webber, an epidemiologist with the Centers for Disease Control in
Atlanta, Georgia, says new treatments to fight antibiotic-resistant bugs are
needed urgently. 鈥淣ovel therapies such as bacteriophages may well be useful,鈥� he
says.
