Searching for less drastic therapies, Stewart and his colleagues are studying how biofilms function in the chronic foot ulcers of diabetes patients. They hope that if they find a topical therapy that works against these surface infections, which are easier to experiment with than are internal biofilms, it might also effectively combat biofilm infections on implants.

Other scientists are exploring ways to prevent biofilms from forming on implants, rather than trying to kill them after they develop. One pioneering technique, developed at the Centers for Disease Control and Prevention (CDC), uses bacteria-destroying viruses known as phages. Phages are strain-specific—in other words, each strain of S. epidermidis would need to be attacked by its own phage. So implants would have to be coated with several phages to fight the multiple kinds of staph that may form a biofilm, explains Rodney Donlan of the CDC. There is always the danger too that bacteria will develop resistance to their phages, and scientists don’t know how the human immune system will react to phage-coated implants. Phages are, after all, viruses and could prompt an immune response that might carry unknown risks. Still, Donlan is optimistic, pointing out that in the countries of the former Soviet Union, phage-based antibacterial therapy has been used successfully for decades.

Coating implants with antimicrobial agents may reduce but not entirely prevent the formation of biofilms and would be particularly ineffective against those caused by antimicrobial-resistant strains.

Some of the same issues affecting doctors trying to treat infected implants also bedevil clinicians treating run-of-the-mill infections. Biofilms have been implicated in middle-ear infections and in persistent urinary tract and prostate infections. Finding a way to break up the biofilm to expose the bacteria within or developing the means to penetrate the protective matrix could help in treating these infections. But researchers are still a long way from finding safe, practical treatments.

Nonetheless, our growing understanding of the natural history of bacteria—and their propensity to live enmeshed within a physical and even a social structure—has far-ranging implications. Researchers’ discoveries about biofilms during the past two decades are already challenging many assumptions and may eventually alter the ways we think about, and defend ourselves against, these strange and ubiquitous forms of microbial life.


  Dossier

1.“Biofilms: City of Microbes,” by Paula Watnick and Roberto Kolter, Journal of Bacteriology, May 2000. An unusually illuminating scientific review comparing biofilms to human cities—complete with suburbs, residential districts and “zoning regulations” governed by bacterial communication.

2.“Self-generated diversity produces ‘insurance effects’ in biofilm communities,” by Blaise R. Boles, Matthew Thoendel and Pradeep Singh, Proceedings of the National Academy of Sciences, Nov. 23, 2004. Explains how rapidly developing genetic diversity in P. aeruginosa biofilms (one of the most harmful, in humans) acts as an “insurance policy” for the biofilm as a whole, in the same way that a diverse population of trees benefits all trees in a forest.

3.“Interspecies communication in bacteria,” by Michael J. Federle and Bonnie L. Bassler, The Journal of Clinical Investigation, November 2003. Difficult but fascinating reading on how autoinducers facilitate interspecies bacterial communication. Learning to interfere with the signal might produce novel therapies to prevent biofilm formation.