Chocolate Agar: Enriched Growth Media in Microbiology

Comprehensive vocabulary flashcards covering the definition, composition, variations, applications, and limitations of Chocolate Agar as discussed in the microbiology lecture.

Chocolate agar

A type of enriched growth medium used in microbiology to culture fastidious bacteria; it contains NO chocolate but is named for its brown color resembling chocolate.

Fastidious bacteria

Organisms that require specific nutrients and do not grow well on standard blood agar, such as Haemophilus influenzae and Neisseria species.

Key Composition of Chocolate Agar

Heated blood agar that lyses red blood cells, releasing essential nutrients like Hemoglobin and NAD.

NAD

Nicotinamide adenine dinucleotide; an essential nutrient released from lysed red blood cells in chocolate agar.

Standard Chocolate Agar

Contains lysed red blood cells providing nutrients for bacteria like Haemophilus influenzae and Neisseria species.

Chocolate Agar with Bacitracin

A variation used to inhibit the growth of certain bacteria and select specifically for Haemophilus species.

Chocolate Agar with IsoVitaleX

Enriched with additional growth factors to support more fastidious organisms and challenging cultures.

Haemophilus influenzae

A bacterium requiring X & V factors that produces grey colonies on chocolate agar.

Neisseria gonorrhoeae

The causative agent of gonorrhea that requires enriched media like chocolate agar for growth.

Neisseria meningitidis

The causative agent of meningitis that can be cultured from cerebrospinal fluid (CSF) samples on chocolate agar.

Streptococcus pneumoniae

A respiratory pathogen that grows on chocolate agar.

X & V factors

Specific growth factors required by Haemophilus influenzae for cultivation.

Colony Appearance

Almost all organisms on chocolate agar produce GREY colonies of various sizes.

Incubation Temperature

The required temperature range for culturing organisms on chocolate agar is $35\text{--}37^{\circ}C$.

Atmospheric Conditions

Chocolate agar cultures require an atmosphere of $5\%\,CO_2$ or a candle jar.

Lack of Differential Properties

A limitation of chocolate agar where it cannot differentiate lactose fermenters like MacConkey agar does.

Thayer-Martin Agar

A selective medium used in parallel with chocolate agar when specific isolation of N. gonorrhoeae is desired.

Blood Agar Plate (BAP)

An enriched medium used for general cultivation with low selectivity, which some fastidious organisms will not grow on.

MacConkey Agar

A differential culture medium used for Gram-negatives that possesses medium selectivity.