What are Microbial Biofilms?

Microbial biofilms have been defined in a number of ways over the last twenty years. New discoveries relating to microbial biofilms are occurring on a regular basis, so the definition of a biofilm will likely continue to evolve for years to come. For the time being, a biofilm has been defined in one respect as "a group of microorganisms binding to a surface and between themselves through a polysaccharide matrix that protects them and makes them extremely resistant" and also as "...a thin, usually resistant layer of microorganisms (such as bacteria) that forms on and coats various surfaces (such as catheters or water pipes)". Leading biofilm scientists have defined a biofilm as "...a structured community of bacterial cells enclosed in a self-produced polymeric matrix and adherent to an inert or living surface." *
* Costerton, JW, Stewart, PS, and Greenberg, EP (1999) Bacterial Biofilms: A Common Cause of Persistent Infections. Science. 284(5418):1318

High-Rise Cities of the Microbial World

This animated movie (to the right) provides a realistic view of the three-dimensional architecture of a Pseudomonas aeruginosa biofilm, which is much like a city made up of high-rises with curving, rather than flat, surfaces. Bacterial biofilms are present on most moist or wet surfaces in nature, though once formed, they are often able to survive very dry conditions. Studies of biofilms have revealed elaborate levels of organization within the biofilm, including differentiated cells, structured groups of cells, and channels that facilitate transport of water and nutrients.

Developed at the Center for Biofilm Engineering at Montana State University, this movie consists of multiple images captured by confocal scanning laser microscopy (CSLM), using FM 1-43 stain. When placed in high-shear conditions, such as within water rapidly flowing in a stream, against a ship’s hull, or through a pipe, these biofilm structures tend to bend, stretch, and become even stronger to withstand the forces of fluid flow. The resilience and adaptability of biofilms to environmental stresses is responsible for many of the negative characteristics of biofilms related to infection, and to biofouling.

Biofilms vs. Disinfectants:
Persistence is Their Key

This animated movie (to the right) shows a computer model time-lapse simulation of a developing biofilm.  At the 100-hour time point, the biofilm is placed in continuous contact with a disinfectant for 15 hours. This should be more than enough time for a disinfectant to kill any bacterial life. As the animation continues, “persister cells” (low metabolic rate cells protected deep within the biofilm) are seen to have a profound influence promoting the survival of the biofilm. This movie demonstrates the remarkable resistance of microbial biofilms to disinfectants and other chemical agents, including most antibiotics.

In this time-lapse simulation of a developing biofilm, green cells represent living bacterial cells within the biofilm. Red cells represent dead bacterial cells within the biofilm, as a result of 15 hours direct contact with a disinfectant.