|
Trillions of bacteria and other microorganisms
are known to dwell happily in the human body. But exactly
how they are able to live their days in obscurity, unbothered
by the immune system, is unknown. Now scientists have some
clues.
In experiments with the intestinal bacteria
known as Bacteroides fragilis, the researchers found that
gut flora may be able to
change their surfaces to avoid detection by the immune system.
The bacteria produce at least eight different
sugars, or polysaccharides, on their surfaces. And this shift
of outerwear could perhaps act as a disguise.
These eight distinct polysaccharides
are the most yet seen on any type of bacteria.
Exactly how the immune system normally
reacts to the body's population of microorganisms, or flora,
is unclear. In fact, the whole area is a "huge black
box."
Clearly, these flora do good things,
such as competing with invading microbes that cause disease.
But they can occasionally get involved in the disease process.
For instance, if there is an injury to the intestines that
causes flora to leak they can cause infection.
It is possible that if the immune system
were primed to attack Bacteroides organisms with a particular
polysaccharide, the microbes
could put on a different surface sugar to allude detection.
The organisms are obviously quite good
at staying alive since they withstand invading germs, bacteria-killing
antibiotics and various "environmental" shifts such
as dietary changes. This study suggests that an occasional
change of wardrobe is one way they do it.
Nature
November 29, 2001;414:555-558
| 