In a cool bit of science they recently published in the journal mBio, the researchers describe how they created a microbial community in a lab dish that mimics what happens in the lining of the human nose and upper throat.
Normally S. pneumoniae bacteria organize themselves there into a stable and highly structured slick, or biofilm, with other microbes, Hakansson says. "You'll see towers growing up," he says, "with channels coming down for water and nutrients," all layered atop the human cells.
Layer by honeycombed layer, a bunch of S. pneumoniae bacteria are building a towering biofilm city atop epithelial cells — the sort that line the throat.
Laura Marks/State University of New York at Buffalo
But when the scientists added a pinch of flu virus to the mix – or in several other ways tweaked the little ecosystem to mimic what happens to the body when we catch the flu – the bacteria changed dramatically.
Increasing the colony's temperature (mimicking the fever of flu), for example, or adding the stress-linked hormone norepinephrine prompted some of the microbes to abruptly break off from the community.
And as they dispersed, the bacteria switched on a set of genes that made each one far more virulent when the scientists squirted them into mice. (In contrast, squirts of bacteria taken from the stable colonies of S. pneumoniae migrated to the animals' throats and harmlessly set up shop there, just as they usually do in people.)
Hakansson says he suspects, though can't say for certain, that the lungs and middle ears are just cul-de-sacs where the activated, pioneering bacteria get stuck during their hunt for a new home in a healthier host. The fact that their human host gets very sick or even dies from such infections isn't good for the bacteria either.
At any given time, between 25 and 40 percent of children under age 5 are colonized with the bacteria, Hakansson says, and between 8 and 15 percent of adults. Typically, these bacterial campsites persist for a few days, weeks or months, and don't produce symptoms. "They don't mean to make us sick," Hakansson says.
Find that cold comfort? You can boost your defenses. The Centers for Disease Control and Prevention recommends that all children under age 5, adults with certain risk factors, and all adults 65 or older get vaccinated against the microbe.