Blood Agar and Vinegar
Date: Winter 2011-2012
I am testing hand sanitizer brands on blood agar plates and comparing their antimicrobial activity to distilled vinegar. When I put a couple of drops of vinegar on the innoculated blood agar plate, the blood agar turned brown. Why?
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The pH of the blood agar was lowered (made more acidic) by adding vinegar.
The protein in blood that makes it red is called hemoglobin. Vinegar is an acid with a relatively low pH. Hemoglobin is adapted to working at your body's natural pH which is about 7.3-7.4. Protein denatures at pH's out of the normal range. The vinegar is probably denaturing the hemoglobin in the blood in the agar plates. The evidence of this is turning the blood brown.
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Update: June 2012