Organisms grown on MacConkey Agar at 37 degrees for 24 hours.
-Important Ingredients: crystal violet, bile salts, neutral red (color indicator), lactose
-Differential: used to identify and isolate lactose fermenting G- enteric bacteria mainly Enterobacteriaceae. Strong lactose fermentation produces pink colonies with bile salt precipitation (hot pink). Weak fermentation produces pink colonies.
-Selective: crystal violet and bile salts inhibit G+ growth and some G- bacteria.
(A): E. coli: strong lactose fermentation resulting in bright pink halo (bile ppt) and pink growth.
(B): Salmonella arizonae: organism can grow but does not ferment lactose, white transparent colonies, turns agar yellow.
(C): Enterobacter aerogenes: ferments lactose, colonies are pink.
(D) Proteus vulgaris: organism can grow but does not ferment lactose, white transparent colonies, turns agar yellow.