Treatments

Bacterial Battles Can Favor The Rise Of Virulent Strains

mouse i i

hide captionWhat's happening inside my nose?

iStockphoto.com
mouse

What's happening inside my nose?

iStockphoto.com

With all the bacteria living inside us, is it any wonder they aren't always the best neighbors?

A scientist experimenting with mice in the U.S. and a biologist in England theorizing on bacterial interactions decided to take a closer look at the microbes' battles for real estate inside our bodies.

They found that the fight for space can favor more dangerous strains.

To figure it out, the scientists set up a three-way competition inside the nose of a mouse: Haemophilus influenzae and two types of Streptococcus pneumoniae.

To elbow S. pneumoniae out of the way, H. influenzae cheats a little by calling up white blood cells in the host to help attack its rivals.

The S. pneumoniae don't take that lying down. Some of them have protective capsules which can ward off attacks from the white blood cells. British evolutionary biologist Sam Brown calls these thick sugar capsules "disguises."

To keep the competition simple, the scientists tested two different S. pneumoniae, each with its own type of capsule. Once they washed the noses of the mice and grew the bacteria they had collected in petri dishes, they found that the balance of the two types was tipped in favor of the more viruluent S. pneumoniae.

"The characteristics that allow [S. pneumoniae] to survive in competition are the same characteristics that allow it to cause disease," American infectious disease researcher Dr. Jeffrey Weiser tells Shots.

About 20 to 30 percent or more of humans carry these bacteria. We don't always get sick from them, but when the bacteria do duke it out, the risk of falling ill with meningitis or pneumonia goes up.

About 1.6 million people per year die of diseases caused by S. pneumoniae, says Weiser. Most of those deaths are cases of pneumonia in young children.

So far, the study, which appears in Current Biology, involves a simple competition model that doesn't include lots of other factors.

Brown says he's curious to know how antibiotics or vaccines might affect the mix. In other words, he asks, "what happens when we add a doctor into this micro-system?"

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