Bacteria use host's immune response to their competitive advantage

Millions of bacteria live within the recesses of our noses and upper respiratory tracts, waiting for a chance to infiltrate and infect. But long before these bacteria break through our immune defenses, they must first compete against other bacterial species to colonize the mucus-lined surfaces of our noses.

Competition between two common nose bacteria involves some interesting trickery, according to a new study in PLoS Pathogens. "We're looking at how bacteria use their host, and we've found that the presence of one species leads to the elimination of another," says Jeffrey Weiser, coauthor of the study and professor of pediatrics and microbiology at the University of Pennsylvania, School of Medicine.

In a mouse model, Haemophilus influenzae--a common bacterium that infects children--stimulates the immune system to send out specialized white blood cells that attack its competitor, Streptococcus pneumoniae--a leading cause of pneumonia. "It is striking that the host's response can so completely eliminate the competitor," says Weiser.

The findings also demonstrate how antibiotics and vaccines that target one microbe might inadvertently alter the competitive interactions among other species present.