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nature science
American Society for Microbiology General
Meeting,
Florida, May 2001
Products containing
the antibacterial
chemical triclosan
have had a bad press
lately because of fears
that they may
promote
antibiotic-resistant
bacteria. A trip to the
supermarket suggests
that triclosan may
have been given a
worse name than it
deserves, say
scientists from the
University of
Manchester in Britain.
Peter Gilbert and his
colleagues found that
15 out of 23 products
selected at random
from the shelves of
their local supermarket could select for resistant bacteria in
the same way that triclosan does.
"Bacteria have evolved to cope with natural antibacterials in
the environment," Gilbert told the annual meeting of the
American Society for Microbiology in Orlando, Florida. Shower
gel, mustard and cinnamon flipped the same molecular
defence switch in bacteria that triclosan does. Fenugreek,
pasta sauce and white wine had little effect.
Triclosan interferes with an enzyme crucial to the growth of
bacteria. But it also trips a genetic master switch called the
multiple antibiotic resistance (mar) operon. This activates a
pump in the bacterial cell wall that expels a host of unwanted
chemicals. "It's a bacterium's vomit response," explains
Gilbert.
So, by setting the pump running, triclosan can help bacteria
spew out antibiotics, warns antibacterial critic Stuart Levy of
Tufts University School of Medicine in Boston, Massachusetts.
If the stimulus is strong enough, Levy says, compounds such
as triclosan can leave us with bacteria whose pumps are
running constantly.
But triclosan isn't the only compound that can turn bacteria
into "permanent vomitors", Gilbert argues.
Using a strain of Escherichia coli genetically modified to stain a
different colour when their mar operons were on, Gilbert found
that half of his random shopping-list could stimulate the
efflux receptor. Six of them did so more powerfully than
triclosan.
Gilbert doesn't advocate the use of antimicrobials in
situations where there is no benefit. But he makes the point
that antibacterial critics "could end up throwing the baby out
with the bath water", depriving consumers of a potentially
useful product.
Triclosan opponents such as Levy are unconvinced. "I don't
see a health relevance to his findings," he says, adding that
the point is that antibacterial products are being widely used
in homes, "with consumer expectation being that they're a
benefit. That benefit hasn't been shown but what has been
shown is that there's a risk."
© Nature News Service / Macmillan Magazines Ltd 2001
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