Staining & Biochemical test

KOH STRING TEST
The Gram stain reaction is not always truly indicative of the organisms true cell wall structure. Poorly controlled decolourising can obviously be a source of misleading results, but even with adequate technique some organisms are problematic. For example, some strains of Bacillus or Clostridium consistently stain Gram negative even though they have a Gram positive type cell wall.
Reagents and Materials : 3% Potassium hydroxide
Test Procedure:
Emulsify a loopful of colony and a drop of 3% KOH on a glass slide. Stir the suspension continuously for 60 seconds and then gently pull the loop vertically away from the suspension.
Interpretation Gram negative bacteria produce a viscous mixture and a thread of this viscid material follows the loop for 10 mm or more as it is raised.

Controls :
Positive Any known Gram negative organism
Negative Any known Gram positive organism