- WASHINGTON (Reuters) - It sounds like a good idea -- put a germ-killing
disinfectant in toothpaste and soap to keep kids and adults safe from infection
- Wrong, Boston-based microbiologist Laura
McMurry and colleagues at the Tufts University School of Medicine say.
- McMurry said triclosan, a disinfectant
widely used in products as diverse as kitchen sponges, soap, fabrics and
plastics, is capable of forcing the emergence of "superbugs"
that it cannot kill. And experiments have shown that it may not be the
all-out germ-killer scientists once thought it was.
- Changing just one gene in the E. coli
bacterium allowed it to resist triclosan's effects, McMurry said in a telephone
interview. "We were able to get resistance by simply changing an amino
acid in the target."
- Triclosan is used so widely because it
is what is known as a nonspecific biocide -- it kills all microbes. Like
bleach and alcohol it was believed to interrupt so many cell processes
there was no way any organism could develop resistance to it.
- "It was just kind of thought it
dissolved the membranes. If it does, then you are probably not going to
get resistance. You would have to have a totally different membrane that
would be resistant," McMurry said.
- Most drugs used as antibiotics work on
just a single process. For instance, penicillin stops many bacteria from
building a strong cell wall by acting against one component, known as a
- But this specific action means many bacteria,
including the very common staphylococcus, can resist penicillin. That is
why new generations of antibiotics have had to be developed.
- MORE USE MEANS MORE CHANCE OF RESISTANCE
- The more a drug is used, the more chances
bacteria have to evolve resistance. Unless all the bacteria in an infection
are killed, the ones that survive exposure to a drug will be those that
resist it in some way, while the weaker ones die first.
- Thus, a species of bacteria can evolve
resistance, especially if this happens over and over again.
- Antibiotic-resistant bacteria are becoming
a bigger and bigger problem. They range from penicillin-resistant gonorrhea
to super-strains of staphylococcus that cannot be killed by vancomycin,
the strongest antibiotic available.
- For this reason, doctors are now being
warned to cut back on frequent prescriptions of antibiotics except for
people who really need them, and patients are being reminded to take their
full course of drugs to make sure no resistant bacteria survive to breed
more resistant bacteria.
- But no one had thought this evolutionary
process was a problem with triclosan because it was thought to kill all
bacteria. Then McMurry and her colleagues put this to the test, breeding
bacteria that had various genetic mutations to see if they would resist
- Writing in the most recent edition of
the journal Nature, they said they had found one. It was a gene called
fab1, which is involved in the creation of fatty acids in cells.
- McMurry said this could mean that bacteria
could evolve resistance to triclosan, but she stressed that there is no
evidence so far that this has happened in nature.
- "We did find those triclosan-resistant
mutants in the lab; we have not looked for them out in the real world.
But the point is not that we've proved that it's really happened out there
in the real world, but that there is the potential."
- Considering this, she said, using triclosan
daily in the home -- in products ranging from children's soaps to toothpaste
to "germ-free" cutting boards -- may be unwise.
- "As I understand it, washing hands
with soap, the goal of it is to wash off the bacteria. I think that unless
it's in a setting where you are in a hospital or you are in a home with
a really sick person, I think it is overkill," she said.
- "That's my suspicion. It's putting
a chemical in there that I'm not sure is necessary."
- McMurry has not tested her mutant bacteria
to see if they would resist triclosan in a real-life setting. "The
amounts of triclosan employed in many of the hand soaps are quite high,"
she said. "I can't say with those high amounts that even my mutant
- But there is more than one way to fight
off a drug. Sometimes bacteria evolve their own resistance, but they also
have a habit of meeting and exchanging genes with one another.
- This means resistance to triclosan could
be acquired, and not simply evolved.
- By MAGGIE FOX, Health and Science Correspondent