When bacteria colonize your teeth or any other solid surface, they form slimy yet durable coatings. These so-called biofilms can lead to cavities, infected pacemakers, and other medical problems. Because biofilms are more resistant to antibiotics than lone bacteria are, drugs that prevent biofilms would make many infections easier to treat. Now researchers have taken a step in that direction by starting to pick apart the molecular signals bacteria use to keep in touch.
To begin to understand what happens when bacteria glom onto a solid surface, microbiologist Thomas Silhavy and colleagues at Princeton University investigated a biochemical cascade called the Cpx pathway. Silhavy's team put Escherichia coli bacteria into vials containing tiny glass beads, whose surface is chemically similar to that of many implants. When normal E. coli attach to the beads, they activate the genes that encode the proteins in the Cpx pathway, the team reports in the 5 February issue of the Proceedings of the National Academy of Sciences. This indicates that the Cpx pathway turns on when bacteria sense a surface, Silhavy says.
In a second set of experiments, the team engineered bacteria to lack the Cpx genes. The mutants could not form biofilms, and only a tenth as many stuck to the beads. But the bacteria that did grasp the beads clung too closely to the surface, resembling a pile of dead cells more than a living biofilm. To Silhavy's team, this means the Cpx pathway also helps the bacteria keep the right distance from the surface--an essential factor for forming a strong biofilm.
The study is an important step toward understanding how bacteria form biofilms, especially on medical devices, says Roberto Kolter, a microbiologist at Harvard University. "If a patient is undergoing a problem with infection, we'd like to control that," he says.
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