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March 18
Quick test for Gram Positive bacteria

Q: Is there a quick easy test for gram positive or negative bacteria that does not use the gram staining procedure?
 
A: Most common beer spoilers are gram positive bacteria.  If you see a bacterial colony growing on a petri dish you can use a quick test to screen it for a gram positive reaction.  Place a loop of the colony onto a slide (using sterile technique) and place a drop of potassium hydroxide on the colony.  Using the loop check to see if the colony appears “gooey” or not.  A gooey consistency indicates a gram negative colony while a non-gooey consistency indicates a gram positive.  Perform a proper gram stain to confirm  this is a gram positive organism.

 

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