MacConkey Agar (Cappuccino & Welsh, 2017).
Description. MacConkey agar is selective and differential medium. It is selective for gram-negative bacteria as crystal violet (in MacConkey) inhibits gram-positive organisms. Lactose, bile salts, and pH indicator neutral red in MacConkey agar allow differentiation between coliform bacilli (lactose fermentation produces acidic end-products indicated by red-colored growth and pink medium surrounding growth) and dysentery/typhoid/paratyphoid bacilli (non-lactose fermenters, no acidic end-products, appear tan/clear).
Clinical significance. MacConkey can help differentiate between gram-negative and gram-positive bacteria when trying to culture a pathogen from a wound sample.
Summary of main steps. It is assumed that the reader knows aseptic technique and basic inoculation.
- Using aseptic technique, inoculate a MacConkey agar plate.
- Incubate inverted plate (lid on bottom) at 37°C for 24-48 hours.
- Observe growth.
Reference
Cappuccino, J. G., & Welsh, C. (2018). Microbiology: A laboratory manual.
