Pluck a microbe out of the ground, and it's
likely to be resistant to most antibiotics, a new Canadian
study finds.
Researchers at McMaster University
screened 480 strains of bacteria they took from soil and
tested them against 21 different antibiotics. Every bacterium
was resistant to a number of antibiotics, an average of
seven or more, according to the report in the Jan. 20
issue of Science.
"The density of resistance is surprising,"
said Gerard D. Wright, chairman of biochemistry and biomedical
sciences at the university's Michael G. DeGroote School
of Medicine. "Old compounds, new compounds, it doesn't
seem to matter. They have all sorts of ways to get around
these things."
That resistance doesn't come from exposure to antibiotics
used in medical treatment, Wright noted. It's just the
bacteria's way of surviving in a world full of perils,
he explained, since they are surrounded by competing organisms
that produce their own natural antibiotics.
"This is giving us a glimpse into very complex organisms
that have been living for millions of years," Wright
said. "They have evolved a really complicated set
of strategies that allow them to deal with all sorts of
threats, old threats and new threats."
While overuse or just plain use of medical antibiotics
is known to increase the incidence of resistance, this
study suggests that natural resistance happens without
exposure to those drugs, he said.
"We got bacteria from a number of sources -- urban
environments, agricultural environments, the woods in
northern Ontario that has not seen any use of human antibiotics
-- and the level of resistance was the same," Wright
said.
Most of the genetic mechanisms of resistance seen in
the study were already known, but a few new ones showed
up, he said. The researchers now are doing more detailed
research into the mechanisms by which bacterial alter
their genetic function to fight antibiotics.
The study has two practical applications, Wright said.
"One is to alert clinicians and medical biologists
to new methods of resistance than can emerge in the clinic,"
he said. "And for people who make antibiotics, this
should give them a heads-up about methods of resistance
they may not see in the clinic today, but may see tomorrow.
Clever chemistry might delay resistance being a problem,"
But there is no way to prevent antibiotic resistance
occurring, because the strategies built up over millennia
can't be dodged completely, Wright said. He noted the
researchers found bacteria resistant to telithromycin,
one of the newest antibiotics on the market.
"This will just help delay and inform about resistance,"
Wright said. "It gives people more ammunition to
fight it."
The finding could also help refine strategies for finding
new antibiotics, said Dr. Stuart B. Levy, a professor
of medicine at Tufts University Medical School, and president
of the Alliance for the Prudent Use of Antibiotics.
A close look at the study shows that many microbes defend
themselves by producing enzymes that break down antibiotics,
said Levy, who is also the author of The Antibiotic
Paradox.
"We may not be finding new antibiotics when we go
to the soil to look for them because we don't take into
account that they are being destroyed," he said.
"We may need new techniques to isolate new antibiotics.
Maybe we can do a better job finding them by knowing this."
