Chinks in the Armour of Bacterial Biofilms
David Davies stood at the hospital bedside of his great-aunt, who had recently had all her toes amputated to try to prevent persistent wounds from spreading. It didn’t work; doctors would later amputate both of her feet, and she never returned to her independent life. As Davies thinks back to this episode from his high-school days, “I remember wondering how come, in this era of antibiotics, was it not possible to treat what was obviously, to me, an infection?”. Even today, such non-healing wounds are common in people with late-stage diabetes like Davies’ great-aunt, who have poor circulation, as well as in people with compromised immune systems. Davies, now an associate professor at Binghamton University, says that many doctors treat these debilitating wounds as a problem with the patient, rather than a sign of infection. “There’s no excuse for it,” he says.
Wounds are just one example of the huge impact of bacterial biofilms. The United States National Institutes of Health says that 80% of chronic infections are biofilm related. Unlike the more familiar planktonic lifestyle, in which bacteria float or swim freely, in biofilms they surround themselves with a complex polymeric matrix, better known as slime. As it grows thicker, the film often includes many bacterial species and the matrix develops a complex structure. Traditional antibiotics are often ineffective. We thought we had it all figured out, Davies says, but the past 20 years have shown that researchers are still in the dark ages when it comes to understanding and controlling bacteria.
As biofilms, bacteria routinely foul industrial equipment and medical devices like catheters and implants, where they form dense layers that cling tightly to the artificial surfaces. They also occur naturally within us, most familiarly as dental plaque. In addition, biofilms are increasingly blamed for recurrent and chronic infections. The case is clear for the Pseudomonas aeruginosa lung infections that haunt cystic fibrosis patients and for recurrent middle ear infections of Haemophilus influenzae. But biofilms are also prime suspects in a long list of other itises, including endocarditis, prostatitis, and conjunctivitis.
Researchers have learned much in recent years about the mechanisms that let bacteria establish a beachhead on a surface and work together to form a highly structured matrix that nourishes and protects them. The films are easily seen by electron microscopy on foreign surfaces like catheters. However, definitively establishing a role for biofilms in a particular diseaseor in chronic wounds like those of Davies’ great-auntis difficult, in part because traditional culture and assay techniques work best for planktonic forms. Even as the evidence comes in, however, many researchers are actively seeking unique vulnerabilities of the biofilm state, hoping to control these stubborn films wherever they occur.
Read more: Looking for Chinks in the Armor of Bacterial Biofilms. PLoS Biol 2007 5: e307
Tags: Antibiotics, Bacteria, Biofilms, Biology, Health, Medicine, Microbiology, Science
