KOH test
From Bugwoodwiki
Purpose
For identification of Gram (-) bacteria. This test replaces the Gram stain. It is much quicker and easier to perform than the traditional Gram stain. It is just as accurate.
Materials
- Microscope slide
- Toothpick
- 3% KOH
Instructions
- Place one drop of 3% KOH on a microscope slide
- With a toothpick, transfer a generous amount of bacteria to the drop of KOH.
- Stir
- Raise and lower toothpick off slide
Expected results
- KOH + (Gram -);bacteria will be viscous and form a mucoid string in 15 sec.
- KOH - (Gram +);bacteria do not become viscous or form mucoid strings in 15 sec.
Notes
- Use 24-48 hr cultures
- It is a good idea to use + and - controls
- KOH should be fresh. Discard any bottles with a white precipitate.
- Coryneform bacteria can be Gram variable as cultures age.
References
- Suslow, T. V., M. N Schroth, and M. Isaka. 1982. Application of a rapid method for Gram differentiation of plant pathogenic and saprophytic bacteria without staining. Phytopathology 72: 917 918.
Contributed by
From the Virginia Polytechnic Institute and State University Mediabook; Orignially created by Robert Wick; contributed by Mary Ann Hansen
