Laboratory Investigations in Microbiology

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Chapter 10: Biofilm

While bacterial growth obtained in a laboratory setting typically takes the form of either colonies (on solid media) or cloudiness (in broth), in nature bacterial growth most often occurs as biofilm. Examples of biofilms include dental plaque, slime coatings in sinks and pipes, bacterial growth on catheters and artificial joints, and microbial mats in environments such as Yellowstone National Park.

Establishment of a biofilm. Initially, planktonic (free-living swimming) cells attach to a solid surface using specific attachment molecules. Once attached, the cells undergo a genetic reprogramming. Studies with Pseudomonas aeruginosa have shown, for example, that genes for motility (flagella) get turned off and genes for production of the  sticky exopolymer substance which makes up the matrix of the biofilm get turned on. Cells also slow down their metabolism and growth, alter their communication behavior, and become significantly more resistant to antibiotics, disinfectants, heat, dryness and other predators. Biofilms may consist of just one microbe or be polymicrobial (dental plaque contains 100's of bacterial species).

In this demonstration, you will be able to see biofilms in cultures and in a stained preparation.

Materials & Methods


1. Examine the culture broths of these 5 bacteria. Describe any notable differences .

2. note the presence of a film of growth on the surface of the broth or on the glass surface.

3. Note the presence of planktonic growth (freely swimming/suspended in liquid) and clumped growth (clumps of cells at the bottom of the tube)

4. Take a picture and include with your data sheet (recommended)

5. Read the referenced article "Biofilms: an emerging form of life"


Data Sheet & Review Questions (printable)


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