 |
|
|
|
|
|
|
|
|
 |
| In the battle
against infectious disease, humankind has inadvertently given rise to deadly
enemies. Antibiotic resistance is a stunning example of evolution by natural
selection. Bacteria with traits that allow them to survive the onslaught
of drugs can thrive, re-ignite infections, and launch to new hosts on a
cough. Evolution generates a medical arms race. The bad news is that bacteria
-- with their fast doubling times and ability to swap genes like trading
cards -- evolve quickly. The good news is that in the 150 years since
Darwin, we have grown to understand the rules of the race. But can we win
this war? |
|
 |
|
|
|
|
| |
Question
submittal is now closed. Please go to the forums
to read our panelists' answers to the user questions.
|
|
| |
  |
|
|
|
 Stephen
R. Palumbi is professor of biology at Harvard
University, where he teaches evolution, marine biology,
and molecular ecology, and conducts research on
populations and molecular genetics of marine animals.
He is the author of The Evolution Explosion (2001),
about how evolution, including antibiotic resistance,
is sped up by human technology. |
|
|
Approaches to reducing antibiotic resistance
include undoing current damage, reversing it,
and slowing evolution down. Undoing damage
will often entail new antibiotics that overcome
current resistance. But the basic arms race
still churns, costly in terms of new drugs and
even lives.
|
|
| It is possible in some
cases to reverse evolution -- to encourage
the re-emergence of drug-susceptible bacteria by
removing the selective pressure of drugs.
Resistance mechanisms sometimes generate an energetic
cost, like extra proteins that the bacteria must
make for drug detoxification. In the drug's absence,
non-resistant bacteria replicate faster, and eventually
take over. Unfortunately, few opportunities arise
to take advantage of this tradeoff, because many
bacteria have evolved low-cost antibiotic resistance. |
|
| To slow evolution, we
can reduce selective pressure by avoiding antibiotics
when they are not useful, (e.g., viral infections),
or substituting other anti-bacterial strategies
instead of chemical control. In agriculture,
integrated pest management employs physical reduction
of insect pests and thereby reduces reliance on
insecticides. Hospitals also use this strategy,
except they call it hand-washing. |
|
| Another method is to
change selective pressures periodically by changing
the antibiotic used. This alters the trajectory
of evolution and can delay the day when full resistance
to one antibiotic evolves. |
|
| A third way to slow evolution
is pyramiding, the use of multiple drugs to deliver
a strong killing dose. Evolution only occurs in
a variable population -- when some bacteria
are able to survive an antibiotic dose, but others
are not. In the presence of a drug overkill, there
is no variation -- all bacteria die -- and evolution
slows dramatically. This is what makes triple-drug therapy effective against the HIV virus. |
|
| In the face of rapid
bacterial evolution, all drug strategies are temporary.
But by studiously engineering the evolutionary process,
we can extend the life of powerful drugs, slow the
arms race, and reduce the social and economic costs
of disease. |
|
| (Boldface added.) |
| <
back to intro page |
|
|
|
|
|
|
|
