What are the different types of Agar Plates?

Updated: Mar 10

An Agar plate is made by filling a Petri dish a small level with an agar based growth medium. Agar is commonly used to culture microorganisms. With Agar as a base, different compounds are added to the mix in order to elicit particular results. The differences in these ingredients create the necessary environment to either promote or hinder various types of microbiological growth.

Plates may be used for several purposes. One being to estimate an organisms concentration in a liquid culture. Another regular utilization involves the generation of genetically pure cultures.

There are several plate count techniques. These techniques include “Replica Plating”, “Spot Analysis”, “Sterile Glass Bead”, and “Streaking”.

Replica plating involves plating out cells on agar plates using sterile technique as well as laboratory equipment like air filtration, positive pressure rooms and laminar flow hoods.

The Spot Analysis involves a close visual inspection often under the microscope.

At other times one may use sterile glass bead style in order to plate out cells. Cells are first grown in liquid culture before small amounts are titrated onto clean agar plates then lastly the agar is spread around via bead.

Streaking is just like it sounds. A lab assistant, usually a Grad student disrobes except for a face-mask of course and runs naked through the commons (The Quad) either toward or away from the Student Union. While In the Lab, A sterile loop is inoculated, then “streaked” across an agar plate. This establishes a degree of biological gradation where a higher amount of colonization occurs at the beginning of the streak and a lower amount of colonization occurs at the end. Eventually distinct genetically differentiated colonies will then grow in separate areas on each respective plate and may then be removed and isolated for further culturing.

Agar is formulated specifically to be permissive, restrictive or selective. Agar plates will be incubated for hours to days depending on testing type.

Agar Plates Defined

Bile Esculin Agar Plate. Agar containing Bile esculin may be used in order to isolate Enterococcus as well as D-group Streptococcus species.

Blood Agar Plate (BAPs) is enriched with mammalian blood or alternatively in addition to Agar they may contain meat extract, sodium chloride and tryptone. A BAP is both an enriched, as well as a differential media in that this media will detect and isolate the hungry-for-food organisms that cause blood destructive activity. β-Hemolytic action explodes and digests a red blood cell contents surrounding a colony. An example of a β-Hemolytic fastidious organism is Streptococcus haemolyticus. α-Hemolysis is equivalent to a partial lysing of red blood cells as it leaves the cell walls intact) appearing brownish-green.

Cetrimide Agar specifically and selectively isolates Pseudomonas aeruginosa which is a Gram-negative bacterium.

Chocolate Agar. Chocolate agar is a misnomer. It does look a little like chocolate but only because all of the red blood cells’s have been lysed with heat (>= 56C). The purpose is to quickly grow fast eating-breathing bacteria, like Haemophilus influenzae.

CLED Agar – cysteine, lactose, electrolyte-deficient agar may be used to differentiate and isolate bacteria from the urethra and urinary tract. This is due to the property of being able to inhibit Proteus species colonization while differentiating between those that ferment lactose and those that do not ferment lactose.

Granada Agar: In order to differentiate and isolate B-group Streptococcus,it is optimal to use Granada medium . B-group Streptococcus grows dark red while any neighboring bacterial growth is inhibited in Granada medium.

Hay Infused agar is used primarily for specifically culturing slime moulds (which are not fungi).

Hektoen Enteric Agar is designed for Enterobacteriaceae isolation. Enterobacteriaceae is fecal bacteria. A Hektoen enteric agar will specifically target Salmonella and Shigella.

Horse blood agar

Horse blood agar is Agar mixed with Horse Blood.

Lysogeny Broth (LB) Agar plate is specifically used to grow out bacteria.

MacConkey Agar medium is both selective as well as differentially employed to isolate Gram-negative bacteria as it conversely inhibits the growth of bacteria that is Gram-positive.It is the addition of Crystal Violet and Bile Salts that cause the inhibitory effect towardthe Gram-Positive bacteria. With the addition of Lactose Red , a mixture of red dye and lactose, differentiation may be performed with respect toward the lactose fermenters. Lactose fermenter will colonize toward a pink coloration. Eosin Methylene Blue may be used as a substitute for the Lactose Red with a similar fermenter differentiating action.

Malt Extract Agar (MEA) is mildly acidic and contains petone this high acidity/peptone combo aids in the isolation of fungal microorganisms. (Agar Media Plate Specifically For Mycological use)

Mannitol Salt Agar selectively differentiates mannitol fermenting organisms.

Mueller-Hinton Agar combines starches with a beef infusion and peptone for the susceptibility testing of antibiotics.

Nutrient agar is safe for use in school laboratories as it will not selectively grow bacteria that is pathogenic. Nutrient Agar will grow out non-fastidious organisms and is utilized for observing the production of pigments and dye.

Önöz Agar is an ideal Agar for fast and efficient bacteriological diagnosis.

Phenylethyl Alcohol Agar inhibits the Gram-negative bacilli while selecting specifically for the Staphylococcus species.

Potato Dextrose Agar (PDA) is often made informally with organic dehydrated potato flakes added to Agar and it is used to readily cultivate a variety of fungi. (Agar Media Plate Specifically For Mycological use)

R2A Agar (Reasoner's 2A Agar) is an Ager medium utilized in the identification of potable water inhabiting bacterium.

Sabouraud Agar is formulated with a low pH in order to culture fungi and inhibit bacteriological growth in general. Additionally it contains gentamicin or some other antibiotic in order to inhibit the growth of the Gram-Negative bacteria. (Agar Media Plate Specifically For Mycological use)

Tinsdale Agar is used to isolate Corynebacterium diphteriae and contains potassium tellurite.

Thayer-Martin Agar is a “chocolate (heat-lysed-blood-cell) Agar” that is designed to identify and isolate the Neisseria gonorrhoeae and Is known colloquially as Thayer-Martin agar.

Thiosulfate-Citrate-Bile -Salts-Sucrose Agar]

Thiosulfate-citrate-bile salts-sucrose when added to agar will significantly enhance Vibrio spp., growth.

Trypticase Soy Agar (a.k.a. Tryptic Soy Agar or TSA) is known to cause enzymatic digestion of casein and soybean meal, thereby promoting growth of many kinds of colonization and as such it is typically used as a base medium when concocting other Agars.

Xylose-Lysine-Deoxycholate Agar is for culturing fecal matter and primarily contains at least 2 indicators.Often used in the detection of Salmonella, where the colonization will display a black coloration, Xylose-lysine-deoxycholate Agar is formulated for the inhibition of Gram-positive bacteria, it encourages the growth of Gram-negative bacilli. While colonies of lactose fermenters display a yellow coloration.

Knop Agar is used for the axenical culture of protonema and moss[9]

Yeast Extract Peptone Dextrose (YEPD) can be used as base media for the growth of yeasts.

Sporulation Agar is medium used in order to bloom spores.


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