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Soon,
astronauts onboard the ISS will test a high-tech medical
device that uses primitive enzymes from horseshoe crabs
to diagnose human illness.
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Nov.
16, 2006: Picture this: You're on a mission to Mars,
halfway there from Earth, and you're not feeling well. Your
throat hurts when you swallow, your forehead is hot. You don't
want to get sick or infect your crewmates. Should you take
an antibiotic? If so, which kind?
 With
a new biological laboratory on a chip being developed at NASA's
Marshall Space Flight Center in Huntsville, Alabama, in partnership
with outside researchers, you may be able to get the answer
in as little as five minutes.
The
mini-lab goes by the maxi-acronym LOCAD-PTS, which stands
for Lab-On-a-Chip Application
Development–Portable Test System.
The latest version is a handheld device slated for launch
this December aboard shuttle mission STS-116 for testing on
the International Space Station.
Right:
LOCAD-PTS. Image credit: NASA.
On
Earth, the most reliable method of diagnosing illness is to
take a sample of bodily fluid (throat swab, or blood or urine
sample) and culture them on Petri dishes with different growth
media in a medical laboratory. Culturing decisively reveals
whether an infection is viral (which will not respond to antibiotics)
or bacterial or fungal (which will), Culturing also pinpoints
the species and thus the most effective kind of antibiotic.
"So-called
gram-negative bacteria, such as E. coli and Salmonella,
respond to different antibiotics than gram-positive bacteria,
such as Staphylococcus," explains Ginger N. Flores, LOCAD
project manager at Marshall.
But
cultures can be impractical, chiefly because growing them
takes two or three days—by which time a person might be very
ill, indeed. LOCAD-PTS, on the other hand, is fast: "It
gives results in 5 to 15 minutes," says Norman Wainwright,
the project's principal investigator and director of research
and development at Charles River Laboratories in Charleston,
SC. "And it's very sensitive—it can detect just a single
bacterium."
The
high-tech device relies on four enzymes extracted from the blood
cells of one of Earth's most ancient living creatures: the horseshoe
crab. "The horseshoe crab, a species that has survived
some 300 million years, has a very primitive but sensitive immune
system," Wainwright continues. A single bacterium can be
enough to trigger enzymes in the crab's immune system, which
clot the blood to seal off a wound.
The
enzymes' extraordinary sensitivity and rapid response makes
them widely useful in medical research to test the effectiveness
of drugs and devices. (Withdrawing a bit of blood annually
from horseshoe crabs, which are then returned to the wild,
does not injure the creatures, and so far there is no acceptable
synthetic substitute.)
It
is these horseshoe crab enzymes that allow LOCAD-PTS to be
so small, sensitive, and fast. First, a tiny amount of enzyme
is inserted into tube-like channels and dried. Introducing
any liquid sample to be tested into the channels rehydrates
the enzymes. If the sample includes bacteria, their toxins
trigger the enzymes, which change the liquid's color—the degree
of color change depending on the number of germs.
 Right:
Horseshoe crabs on a beach. Photo credit: University of Delaware.
[More]
The
experiment package scheduled to fly in December will compare
LOCAD-PTS to tried-and-true Petri-dish methods. Once a week
for six weeks, astronauts will press a sticky, flexible patch
onto an exposed surface, and then swab a short distance all
around the patch. Any bacteria adhering to the swab will be
introduced into LOCAD-PTS, whereas any bacteria adhering to
the sticky patch will be cultured. A few days later, bacterial
colonies will counted in the traditional manner.
Note:
This procedure takes advantage of the fact that humans aren't
the only astronauts in space: the surfaces of the space station,
just like walls, floors, and kitchen counters here on Earth,
are rich in bacteria ("one small step for a germ…").
Of course, Wainwright and Flores expect that LOCAD-PTS will
prove to be fast--but what about accurate? A big
unknown is how well LOCAD-PTS will compare in analyzing the
type of bacteria, and how well its color changes can be calibrated
to the number of bacterial colonies that grow. "We also
want to see how easy and practical the device is for astronauts
to manipulate in microgravity," Flores adds.
Although
the initial LOCAD-PTS will test only for Gram-negative bacteria,
"we plan later also to test for Gram-positive bacteria,
yeast, mold, and certain chemicals."
Eventually,
if all goes as planned, one sample from the throat of an ill-feeling
astronaut could be sent flowing through parallel channels
on a future generation of LOCAD-PTS, and could indeed, within
minutes, come up with a diagnosis like "take two Amoxicillin
and call me in the morning."
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Author: Trudy E.
Bell | Editor:
Dr. Tony Phillips | Credit: Science@NASA
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