Subject Area(s) | microbiology |
Intended Audience |
high school biology, independent study/science fair, introductory undergraduate microbiology, advanced college level microbiology |
Type | laboratory exercise |
Revision Date | November 19, 2003 |
Students should be able to define a biofilm, describe the differences between biofilm (surface-attached) and planktonic (free-floating) bacteria, and be able to describe why bacteria usually grow on surfaces. Students should also be familiar with standard methods for serial dilution and plating of microbial cells on standard media. Students must understand the basic premises of bacterial plate counting. It is normally understood that each colony on a plate represents the clonal descendents of a single bacterium. If biofilms are not adequately disaggregated, this assumption may fail. There are a number of methods of disaggregation and some are better than others.
Quantity |
Description |
As Necessary | Wooden applicator sticks, 6 inches long and sterilized by autoclaving (see alternative methods of autoclaving in Notes for Teachers) upright in screw capped tubes [These sticks are used for scraping biofilm from the surface of a slide or coupon (one stick for each student). |
As Necessary | sterile culture tubes with caps (18 x 150 mm) |
As Necessary | phosphate buffered saline (PBS) |
As Necessary | mechanical pipetting devices and sterile pipettes or automatic pipetters, pipettes and pipette tips |
As Necessary | Branson or equivalent sonic cleaning water bath |
As Necessary | microscope slides, coupons or other object with biofilm attached3. [An ideal coupon is made by Erie Scientific Company Portsmouth, NH, 800-258-0834 or www.eriesci.com. These are diagnostic slides with preprinted areas of known dimensions. Using these as coupons, the student can know precisely the area from which cells are being harvested.] |
Pictures of example equipment.
Development of a Standardized Antibiofilm Test
Zelver, N., M. Hamilton, D. Goeres, D. Walker, and J. Heersink, in Microbial Growth in Biofilms: Part B (R.J. Doyle, Ed.): Methods in Enzymology, Volume 337, pp. 363-376 (2001). See page 366 for scraping and plating techniques.
"Biofilm samples from the rotating disk reactor are obtained by aseptically removing the test coupon from the rotor and removing the biofilm with a sterile wooden applicator stick. The stick is stirred vigorously into a test tube containing 9 ml of sterile buffered water. The entire coupon surface is scraped approximately three times for 1-2 min. The coupon is rinsed with 1 ml of sterile buffered water into the original 9 ml, bringing the final volume of the tube to 10 ml. Prior to enumeration, the cells are disaggregated by homogenization at a speed of 20,500 rpm for 30 sec to eliminate biofilm clumps." pp. 366
A reprint of this paper can be obtained by emailing the Center for Biofilm Engineering, publications@biofilm.montana.edu. Request paper 01-021
1A coupon is an experimental surface on which biofilms may be grown. The biofilm may then be examined directly by microscopy or sampled for quantification or to determine its properties.
2Standard methods for the examination of water and wastewater : including bottom sediments and sludges 18th ed. ©1992 American Public Health Association, New York.
3Example exercises of how to grow biofilms on objects can be found at http://www.personal.psu.edu/faculty/j/e/jel5/biofilms/. See Buried Slide Technique, Microbial Fishing.
Supported in part by the Waksman Foundation for Microbiology
Developed in collaboration with Dr. John Lennox, Penn State University-Altoona
© 1999-2008 Center for Biofilm Engineering, http://www.biofilm.montana.edu