Even though you may not be familiar with the term biofilm, you have certainly encountered biofilms on a regular basis. For example, the plaque that forms on your teeth and causes tooth decay is one type of bacterial biofilm. The “gunk” that clogs your household drains is also a biofilm. If you have ever walked in a stream or river, you may have slipped on rocks that were slimy with biofilm. A persistent infection on a scrape you got from a sports injury was likely a biofilm. And so it goes: biofilms—they’re where you want to be.
A biofilm is composed of living, reproducing microorganisms, such as bacteria, that exist as a colony, or community. In other words, biofilms are alive and have a complex social structure that scientists and engineers are still trying to unravel, a structure that both protects them and allows them to grow.
A biofilm forms when certain microorganisms (for example, some types of bacteria) adhere to the surface of some object in a moist environment and begin to reproduce. The microorganisms form an attachment to the surface of the object by secreting a slimy, glue-like substance. Biofilms can form on just about any imaginable surface: metals, plastics, natural materials (such as rocks), medical implants, kitchen counters, contact lenses, the walls of a hot tub or swimming pool (did you ever notice that the sides of a hot tub or swimming pool seemed slightly slimy?), human and animal tissue, and on and on. Indeed, wherever the combination of moisture, nutrients, and a surface exists, biofilms will likely be found as well.
A biofilm community can be formed by a single kind of microorganism, but in nature biofilms almost always consist of mixtures of many species of bacteria, as well as fungi, algae, yeasts, protozoa, and other microorganisms, along with non-living debris and corrosion products. For example, over 500 bacterial species have been identified in typical dental plaque biofilms!
Biofilms can be so thin as to avoid detection by the naked eye—just a few cell layers thick. The biofilms that almost certainly exist on your kitchen counter, for instance, are generally undetectable to the eye (unless, like some college students, you don’t wash your counters very often). They can also grow to become many inches thick; probably not on a countertop (at least we hope not), but certainly as algae on rocks in a streambed.