Columbia-CNA Agar
Columbia-CNA Agar (C-CNA) is a type of selective media which selects for Gram-positive bacteria. It contains two antibiotics, colistin and naladixic acid, which inhibit the growth of gram-negative bacteria, thus selecting for Gram-positive organisms. C-CNA agar also contains whole blood, which allows differentiation based on hemolysis patterns.
Quadrant 1: Growth on the plate indicates this organism, Enterococcus faecalis, is resistant to the antibiotics colistin and naladixic acid and is Gram-positive.
Quadrant 2: Absence of growth on the plate indicates the organism, Enterobacter aerogenes, is sensitive to the antibiotics and is Gram-negative.
Quadrant 3: Absence of growth on the plate indicates the organism, Escherichia coli, is sensitive to the antibiotics and is Gram-negative.
Quadrant 4: Growth on the plate indicates this organism, Staphylococcus aureus, is resistant to the antibiotics and is Gram-positive.