Chocolate Agar: Composition, uses and colony characteristics

Chocolate Agar is the lysed blood agar. The name is itself derived from the fact that Red blood cell lysis gives the medium a chocolate-brown color

The composition of Chocolate agar and the Blood Agar is same and the only difference is while preparing Chocolate agar, the red blood cells are lysed.

The lysis of RBC releases intracellular nutrients such as hemoglobin, hemin (Factor X) and the coenzyme Nicotinamide adenine dinucleotide (NAD or V Factor) in to the agar for utilization by fastidious bacteria.

The most common species that require this enriched medium for growth include: Neisseria gonorrhoeae and Haemophilus spp. Neither of these species is able to grow on Sheep Blood Agar.

Colony characteristics in chocolate agar

  1. Neisseria meningitidis: Growth on chocolate agar is grayish, non-hemolytic, round, convex, smooth, moist, glistening colonies with a clearly defined edge.
  2. Neisseria gonorrhoeae: Colonies on GC-Chocolate agar are pinkish-brown and translucent, exhibit smooth consistency and defined margins, and are typically 0.5-1 mm in diameter.
  3. Haemophilus influenzae: Non hemolytic, opaque cream-to-gray colonies (Accompanying Sheep blood agar shows no growth)

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