SOP: Scotch Tape Method for Surface Counts
GIFSQ — Global Institute for Food Safety & Quality
Principle
Adhesive tape pressed firmly onto a surface lifts the bacteria from it; pressing the used tape onto an agar surface transfers the bacteria to the medium, where colonies grow on incubation and are counted.
Apparatus required
- Scotch tape or similar material (about 2 in. long strips cut from a reel 1 in. wide)
- Petri dishes with agar medium
- Incubator
Reagents
a. Agar medium in Petri dishes.
b. Nutrient agar — To 1,000 ml of distilled water add 10 g of Lab Lemco, 10 g of peptone and 5 g of NaCl (AR). Autoclave at 5 psig for 10–15 min, then set the pH to 8. Filter out any precipitated phosphates. Add agar to 1%, dissolve by steaming or autoclaving, and bring the pH back to 7.4. Bottle the medium and autoclave at 10 psig for 10 min. (The chapter gives this preparation for general bacterial counts; the tape is pressed onto agar medium in a Petri dish.)
Sample preparation
None.
Procedure — Scotch tape surface counts
Cut strips of scotch tape or similar material about 2 in. long from a reel 1 in. wide
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Without handling the sticky surface, place a strip firmly on the surface to be counted
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Peel off the strip
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Press it on the surface of agar medium in a Petri dish
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Peel off and discard the tape
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Incubate the culture medium and count the colonies which grow from the transferred bacteria
Calculation
No calculation is required — report the colony count obtained from the tape transfer.
Precautions
- Do not handle the sticky surface of the tape.
- Press the tape firmly on the surface to be counted so that the bacteria are transferred.
References
- De Man, J.C., Rogosa & Sharpe, J. Appl. Bact. 23, 130 (1960).
- Knox, R. & J. Walker, J. Hyg. Camb., 45, 187 (1947).
- (Author name illegible in the available copy — printed as “Gos) C.H.”), Microbiological Methods, 2nd edn., Butterworth & Co. Ltd., London, p. 347 (year printed as 1997).