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We wish to express our gratitude to our co-workers and apologize that for lack of space we wereunable to present a broader coverage of the field andinclude more references.REVIEWBacterial Biofilms: A Common Cause ofPersistent InfectionsJ. W. Costerton,1Philip S. Stewart,1E. P. Greenberg2*Bacteria that attach to surfaces aggregate in a hydrated polymeric matrixof their own synthesis to form biofilms. Formation of these sessilecommunities and their inherent resistance to antimicrobial agents are atthe root of many persistent and chronic bacterial infections. Studies ofbiofilms have revealed differentiated, structured groups of cells withcommunity properties. Recent advances in our understanding of thegenetic and molecular basis of bacterial community behavior point totherapeutic targets that may provide a means for the control of biofilminfections.For quite some time we have known thatbacteria can adhere to solid surfaces andform a slimy, slippery coat. These bacterialbiofilms are prevalent on most wet surfacesin nature and can cause environmentalproblems. Perhaps because many biofilmsare sufficiently thick to be visible to thenaked eye, these microbial communitieswere among the first to be studied by thelate-developing science of microbiology.Anton van Leeuwenhoek scraped theplaque biofilm from his teeth and observedthe “animalculi” that produced this micro-bial community with his primitive micro-scope. However, it was not until the 1970sthat we began to appreciate that bacteria inthe biofilm mode of existence, sessile bac-teria, constitute a major component of thebacterial biomass in many environments(1), and it was not until the 1980s and1990s that we began to appreciate that at-tached bacteria were organized in elaborateways (2). For example, different bacterialspecies specifically attach to different sur-faces or coaggregate with specific partnersin the mouth (3). Often one species cancoaggregate with multiple partners, whichthemselves can aggregate with other part-ners to form a dense bacterial plaque. Ad-vances in light microscopy coupled withdevelopments in microelectrode technologyhave led to an appreciation that bacterialbiofilms consist of microcolonies on a surface,and that within these microcolonies the bacteriahave developed into organized communitieswith functional heterogeneity.Because bacterial biofilms can cause en-vironmental problems and studies of bio-films have required the development ofnew analytical tools, many recent advanceshave resulted from collaborations betweenmicrobial ecologists, environmental engineers,and mathematicians. These efforts have