Battling Bacteria

Although the public rarely hears it in popular discussions of health issues, the term 8220;biofilm8221; was coined in a 1978 Scientific American article by William Costerton, now of the University of Southern California Dental School. He used it to describe microbes that clump together on wet surfaces.

8220;It came up in dentistry first,8221; Costerton said. 8220;They called it plaque. I just proposed that the biofilm isn8217;t just in the mouth, but everywhere.8221;

Biofilms are just about everywhere. They coat everything from Alpine river rocks to neglected teeth. Every year they cause billions of dollars of damage to ship hulls and pipelines by corroding metal surfaces and clogging up the works.

These plaques often contain a variety of microorganisms, including bacteria, protozoa and algae suspended in slimy glue called polysaccharide that holds them together and binds them to surfaces. When enough of the organisms have collected, they undergo metabolic changes that make them better team players.

Particularly vexing is the ability of virulent bacterial infections to resist attack after forming a biofilm. 8220;We could pump bleach into your system,8221; Shirtliff said, 8220;and it probably wouldn8217;t do anything.8221; That8217;s saying something. Chlorine bleach is the microbiologist8217;s ultimate weapon8212;it8217;s used to disinfect the labs that house the world8217;s most dangerous germs.

Like soldiers hiding in a castle, the bacteria inside the film are protected from drugs designed to kill them. The cells are also starved for nutrients. This makes them grow and divide slowly8212;providing even more drug resistance, since antibiotics often target fast-growing cells.

The stress also puts biofilm bacteria on the defensive, causing them to release caustic acids and proteins. Said Shirtliff: 8220;They turn on stress response genes that make them attack the antibiotic.8221; Compounding the problem, the stress response tricks the immune system. When the macrophages and other white blood cells that form the body8217;s police force arrive on the scene, they8217;re ambushed and destroyed by the biofilm8217;s proteins and acids.

Biofilm infections often return because antibiotics kill only the free-floating bacteria. When a patient stops taking the drug, new free-roaming bacteria emerge from the biofilm and the infection spreads again.

Scientists estimate that 65 percent to 80 percent of chronic infections in industrialised nations linger on because of biofilm formation. Biofilms appear in patients with cystic fibrosis, gum disease and chronic inner ear, urinary tract and bone infections. Medical devices such dental implants, catheters, artificial joints and heart valves are vulnerable to biofilm formation.

The trick, Shirtliff believes, is to hone in on the odd behaviour of the biofilm bacteria. He has identified proteins they produce in abundance as they form a film and hopes to develop antibodies to target those proteins. Like an army attacking a half-built fortress, the antibodies would attack the immature biofilm and destroy it.

Chris Emery

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