Agar plate

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An agar plate streaked with microorganisms isolated from a deep-water sponge.

An agar plate is a sterile Petri dish that contains agar plus nutrients (media), used to culture microorganisms. Generally, selective growth compounds are also added to the media, such as antibiotics.

For information on agar plate preparation, please visit the .

Contents

1 Types of agar plates

1.1 Blood agar types
1.2 General bacterial media
1.3 Fungal media

2 References
3 See also
4 External links

Types of agar plates

Four types of agar plates demonstrating differential growth depending on bacterial metabolism.

A subset of commonly used agar plate types is listed below.

Blood agar types

Blood agar plate (BAP)

Contains blood from a mammal (usually sheep), and respires to typical transperent nature, typically at a concentration of 5–10%. BAP are an enriched, differential media used to isolate fastidious organisms and detect hemolytic activity. β-hemolytic activity will show complete lysis of red blood cells surrounding colony, while α-hemolysis will only partially lyse hemoglobin and will appear green. γ-hemolysis is the term referring to a lack of hemolytic activity.

Chocolate agar (CHOC)

A type of blood agar plate in which the blood cells have been lysed by heating the cells to 56 °C; used for growing fastidious (fussy) respiratory bacteria.

Thayer-Martin agar (TM)

Chocolate agar designed to isolate Neisseria gonorrhoeae.

General bacterial media

Bile Esculin Agar (BEA)

BEA is used for the isolation of Enterococci as well as Group D Streptococci

Hektoen Enteric (HE)

HE agar is designed to isolate and recover fecal bacteria belonging to the Enterobacteriaceae family. HE is particularly useful in isolating Salmonella and Shigella.

MacConkey agar (MAC)

A selective and differential media used to differentiate between Gram negative bacteria while inhibiting the growth of Gram positive bacteria. The addition of bile salts and crystal violet to the agar inhibits the growth of most Gram positive bacteria, making MacConkey agar selective. Lactose and neutral red are added to differentiate the lactose fermenters, which form pink colonies, from lactose nonfermenters that form clear colonies.

Mannitol Salt Agar (MSA)

MSA is also a selective and differential media. Mannitol is the differential part, it indicates organisms that ferment mannitol. If mannitol fermentation is occurring, lactic acid will be produced, and the pH will drop causing the MSA plate to turn yellow. The salt portion is selective for halophiles; organisms that cannot withstand a high salt content will be unable to grow.

Nutrient agar

Safe to use in school science laboratories because it does not selectively grow pathogenic bacteria.

Önöz agar

Önöz agar allows more rapid bacteriological diagnosis as Salmonella and Shigella colonies can be clearly and reliably differentiated from other Enterobacteriaceae. The yields of Salmonella from stool samples obtained, when using this medium, are higher than those obtained with LEIFSON Agar or Salmonella–Shigella agar (SSA).

Phenylethyl Alcohol Agar (PEA)

PEA selects for Staphylococcus species while inhibiting Gram-negative bacilli (e.g. Escherichia coli, Shigella, Proteus, etc.).

Tryptic (Trypticase) Soy Agar (TSA)

TSA is a general purpose media produced via enzymatic digestion of soybean meal and caesin; TSA is frequently the base media of other agar plate type, i.e. blood agar plates (BAP) are made by enriching TSA plates with blood (see above).

TSA plates support growth of many semi-fastidious bacteria, including some species of Brucella, Corynebacterium, Listeria, Neisseria, and Vibrio.

Xylose-Lysine-Deoxycholate (XLD) agar.

XLD is used for the culture of stool samples, and contains two indicators. It is formulated to inhibit Gram-positive bacteria, while the growth of Gram-negative bacilli is encouraged. The colonies of lactose fermenters appear yellow.

Fungal media

Fungi growing in axenic culture (ascomycetes)

Sabouraud agar

Used to culture fungi, Sabouraud agar and has a low pH that inhibits the growth of most bacteria; also contains the antibiotic gentamicin to specifically inhibited the growth of Gram-negative bacteria.

Hay Infusion agar

Specific for the culturing of slime moulds.

References

External links

[All About Agar]

Laboratory equipment

Laboratory glassware

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