Fig. 6: Uninoculated Plate of MacConkey Agar

MacConkey agar is a selective medium used for the isolation of non-fastidious Gram-negative rods, particularly members of the family Enterobacteriaceae and the genus Pseudomonas, and the differentiation of lactose fermenting from lactose non-fermenting Gram-negative bacilli. MacConkey agar contains the dye crystal violet well as bile salts that inhibit the growth of most Gram-positive bacteria but do not affect the growth of most Gram-negatives.

Photograph from From
Courtesy of David Miller and Patrick Hanley, Hartwick College, Oneonta, NY.