If you observed growth of gram negative organisms on the PEA

If you observed growth of gram negative organisms on the PEA plate you inoculated does this negate the usefulness of PEA as a selwctive medium

Solution

PEA is a media use for culturing gram positive bacteria and it is selsctive for only Gram positive bacteia because polyethylene alcohol inhibit the growth of gram negative bacteria by inhibiting their DNA syntheis and distrupting the lipid membrane present in the gram negative bacteria. The growth of gram negative bacteria in PEA plate shows the grwoth of obligatory anearobic gram negative bacteria (they are gram negative but anearobic bacteria which grows only in the absence of Oxygen and PEA is a aneaobic media)