I.
Alternative test for Gram Reaction – 3%
Potassium Hydroxide
A.
Add a heavy inoculum of pure culture of bacteria grown on a solid
medium to a drop of 3% potassium hydroxide (KOH) solution (3 grams KOH per 100
mL distilled water) on a clean glass slide.
B. Stir for about one minute,
occasionally lifting the loop to look for thickening and “stringing” of the slurry.
1.
Gram positive: bacteria will not appear to change the viscosity of the KOH solution.
2.
Gram negative: bacteria will cause the KOH solution to become stringy or mucoid in appearance and consistency.
D. QUALITY CONTROL:
1.
Gram Positive: Staphylococcus sp.
2.
Gram Negative: Escherichia coli
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