Chocolate Agar- Composition, Principle, Preparation, Results, Uses


Chocolate agar is a type of culture medium that is used to grow bacteria that are difficult to cultivate with ordinary media. It is especially useful for isolating and identifying fastidious pathogens, such as Haemophilus influenza and Neisseria meningitides, which cause respiratory infections and meningitis.

Chocolate agar is a variant of blood agar, which contains red blood cells that provide nutrients for bacterial growth. However, unlike blood agar, chocolate agar is prepared by heating the blood agar to 80°C, which causes the red blood cells to lyse (break down) and release their contents into the medium. This process gives the medium a chocolate-brown color and also makes it enriched with hemoglobin, hemin (X factor), and nicotinamide adenine dinucleotide (NAD or V factor), which are essential for the growth of some bacteria.

Chocolate agar is a non-selective medium, meaning that it can support the growth of many types of bacteria. However, it can be modified by adding antibiotics or other supplements to make it selective for certain bacteria. For example, chocolate agar with bacitracin can select for Haemophilus species, while chocolate agar with vancomycin, nystatin, and colistin can select for Neisseria species.

Chocolate agar is widely used in clinical microbiology laboratories for the isolation and identification of bacteria that cause serious infections in humans. It is also used for quality control and susceptibility testing of these bacteria. Chocolate agar is easy to prepare and has a long shelf life compared to other media.

In this article, we will discuss the composition, principle, preparation, results, uses, and limitations of chocolate agar in detail. We will also explore some of the modifications of chocolate agar that are available for different purposes.