Phenylethyl Alcohol (PEA) Agar

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Purpose:  A selective medium used to inhibit the growth of Gram negative organisms.   Principle:  PEA prevents the growth of Gram-negative organisms by disrupting the sturcture of lipids in the Gram-negative membrane.  It also can hamper protein synthesis.  PEA is present in this medium at 0.025%, if the concentration was higher it would affect both Gram positive and Gram negative cells. The plates to the right illustrate PEA inhibition of Gram-negative cell growth.  Plate A is a PEA plate with a Gram positive organism on the left and a Gram negative organism on the right.  Plate B is a nutrient agar plate illustrating normal growth of each of the same bacteria.  Notice that the Gram-negative organism shows inhibited growth on the PEA plate.

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Lab Procedures

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