Purpose: To isolate and differentiate between various members of the family Enterobacteriaceae.
Principle: DOC contains sodium deoxycholate and citrate which work to inhibit the growth of Gram-positive organisms. The medium also contains the sugar lactose, which serves to differentiate among enterics that ferment and do not ferment lactose. Fermentation of lactose appears as a red color due to the pH indicator neutral red, which is included in the medium.
The plate to the right shows common reactions observed on a DOC plate. The reactions are as follows.
A. Heavy lactose fermentationB. Reduced growth of a Gram-positive organism
C. No lactose fermentation
D. Light lactose fermentation
