Invader. S. pneumoniae (red) colonize nasal tissue (green).

Battle of the Bugs

The inside of our nose resembles a crowded subway car at rush hour. Millions of microbes jostle for seats, but only a select few will get settled. Now scientists have uncovered a clever mechanism by which Haemophilus influenzae, a bug that commonly instigates childhood sinus infections, uses the body's immune response to crush its competition.

Our bodies tolerate a wide range of resident microbes, but when these bugs grow out of control, the immune system hits them with a slew of fighter cells. Haemophilus and its rival, the pneumonia-causing Streptococcus bacteria, compete for the same niche in children's noses. Therefore, researchers surmised that there must be some push and pull between the two organisms for one to eventually prevail over the other, as happens during an infection.

Jeffrey Weiser and colleagues at the University of Pennsylvania School of Medicine in Philadelphia turned to mice to figure out how this happens. Until now, scientists thought that, given a head-to-head battle, Strep would win out; that's what always seemed to happen in the Petri dish. But when the team grew the bugs together in mouse nasal passages, the mouse's immune cells killed off the Streptococcus strain. The team went on to show that Haemophilus somehow recruited host immune cells, called neutrophils, to the site of colonization. These cells specifically targeted and eliminated the Streptococcus bacteria but left its competitor relatively intact, the researchers report in an upcoming issue of the Public Library of Science journal PloS Pathogens.

This is very important data that shows how a host's response can influence bacterial colonization, says David Briles, a microbiologist from the University of Alabama in Birmingham. But these are probably very specific responses, he cautions, so what you see in mice may not be exactly what you see in people.

Related site
Weiser's Web site