Bacteria are sticky—so sticky that we schedule regular appointments with professionals to scrape them off our teeth. Dental plaque may be the best-known example of a biofilm, but these slimy aggregates of bacteria also play major roles in such chronic infections as those in the urinary tract or in the lungs in cystic fibrosis patients. The problem? Antibiotics often can't penetrate the slime to get at (and destroy) the pathogenic bacteria cocooned within.
To build a biofilm, bacteria secrete stringy sugars, proteins and DNA fragments into what effectively becomes a defensive mesh around the microorganisms—making the structures the microbial world's equivalent of “walled cities,” according to structural biologist Perrin Baker of Toronto's Hospital for Sick Children. He and his colleague Lynne Howell have been working on methods to dismantle these structures. “What we want to do is create chinks in the wall to allow the invading army in,” Howell explains.
To make these cracks, the researchers turned to Pseudomonas aeruginosa—a bacterial species that often builds biofilms within the lungs of cystic fibrosis patients, which can lead to chronic obstructive pulmonary disease and subsequently death. P. aeruginosa produces several different enzymes that can clear away overgrown or tangled biofilm sugars so the bacteria can navigate the structure themselves. Baker and Howell wanted to see if they could turn these enzymes to their advantage. They first extracted two biofilm-pruning enzymes from the microbes and then added them to petri dishes coated with biofilms. As recently reported in Science Advances, the researchers found that the enzymes destroyed most of the sugary infrastructure built by several different Pseudomonas strains. With one strain, for example, 94 percent of the biofilm's mass dissolved on contact with the enzymes.
Even though the enzymes tear down large sections of the biofilms, the bacteria within are left unharmed. So the method “wouldn't be a magic bullet” on its own, says Stanford University infectious disease expert Paul Bollyky, who was not involved in the study. Yet it does leave the vast majority of bacterial residents exposed and therefore vulnerable to a follow-up round of antibiotics or the natural attacks of the body's immune system.
The researchers will next try to find out whether the enzymes are as successful at combating biofilms in the lungs of mice as they are in petri dishes. Baker is also interested in seeing if coating hospital equipment with sugar-cutting enzymes could help prevent the formation of drug-resistant germs.