Bacteria are often pictured as lone cells moving randomly about. In fact, millions of bacteria frequently stick together in well-organized colonies. This is slime-or, as microbiologists prefer to call it, “biofilm.” A research team at the Center for Biofilm Engineering at Montana State University (MSU) in Bozeman has now identified the chemical signal secreted by bacteria that tells the microbes when to form-and when to desert-these bacterial structures.

The discovery could provide clues on ways to shut down the formation of biofilms. And that could mean a potful of applications-including controlling bacterial infections in hospitals and controlling contamination of water supplies. As a result of these implications, the findings “are of considerable significance,” says molecular geneticist John Geiger, group leader for biotechnology at Olin, a Cheshire, Conn.-based producer of industrial biocides.

The MSU group, headed by microbiologist David Davies, found that a common bacterium, Pseudomonas aeruginosa, secretes a chemical called homoserine lactone (HSL) that controls the development of biofilms.They suspect that biofilms created by other types of bacteria also depend on the chemical signal.
Based on the insight, the MSU group is already synthesizing and testing chemicals that disrupt the natural messenger system. And while the work is still in the early stages, the possibilities are almost endless. Biofilms grow anywhere there’s water and a hard surface, forming mushroom-shaped pillars with protective slimy coatings.

Biofilms create countless medical problems, contaminating contact lenses, catheters and artificial implants. Biofilms of P. aeruginosa pose particular concerns-they are the chief cause of hospital-acquired infections; they also clog the lungs of cystic fibrosis patients. Another biofilm, dental plaque, corrodes teeth and is an obvious target. A chemical based on HSL “could be added to toothpaste or mouthwash,” says microbiologist Bill Costerton, director of the Center for Biofilm Engineering.

Industrial water systems, a haven for biofilms, could also be made slime-free by pouring in compounds that block bacterial congregation. Likewise, the MSU results could lead to safer chemicals to prevent biofouling on boats, replacing biocide paints that contain toxic heavy metals.

The long-held trend to kill problematic bacteria using antibiotics and biocides “has caused all kinds of problems like bacterial resistance. Now we can’t even kill them,” says Costerton. “Perhaps we can coexist with bacteria and manipulate their bothersome ways.” Learning how to prevent them from forming their bacterial cities may be a first step in that direction.