Microbiology Growth Media

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    Describe this growth medium.
    Blood Agar Plate

    • General purpose for variety of organisms
    • - contains RBCs which provide nutrition

    Differential pattern of hemolysis
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    Type of Hemolysis?

    • Microbe produces H2O2
    • Leads to oxidation of Hb in RBCs
    • Hb --> methemoglobinperoxide (green color)
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    Type of Hemolysis?

    • Microbe completely digests RBCs, clearing the agar
    • Organisms produce hemolysin which lyses RBCs

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    Type of Hemolysis?

    • No hemolysis of the RBCs in agar
    • Microbes do not produce enzymes to digest RBCs
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    Describe this growth medium.
    Chocolate Agar

    • Blood agar with RBCs pre-lysed by heating
    • - provides easier access to nutrients
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    What are the two reasons to use this agar?
    Chocolate Agar

    • Good for microbes with hard to meet needs that cannot hemolyze RBCs, like
    • - Haemophilus sp.
    • - Neisseria sp.

    Thayer-Martin: selective version with added antibiotics to detect N. ghonorrhoeae
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    Describe the composition of this medium (began pink).
    Mannitol-Salt Agar

    • A selective media due to high [NaCl]
    • Pink color is a pH indicator (turns yellow on pH drop)
    • Mannitol is diagnostic nutrient
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    Organisms that grow on Mannitol-Salt Agar
    High [NaCl] selective for Staphylococcus species

    - S. aureus: ferments mannitol, decreasing pH and changes agar from pink to yellow

    - other Staphylococci: do not ferment mannitol, leaving agar pink; still capable of growth
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    Describe the composition of this medium (began yellow).
    MacConkey Agar

    • Contains bile salts, crystal violet, and neutral red dye
    • Lactose is sole carbohydrate
    • Also contains peptones (source of amino acids, carbons)
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    What is MacConkey agar used for?
    Bile salts and crystal violet inhibit Gram+

    • Selects for most Gram Neg bacteria
    • - Fastidious G- (e.g. Neisseria, Hemophilus) do not grow well

    • Color indicator
    • - Lactose-fermenters pick up dye, turn pink or red
    • - Non-fermenters remain clear
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    Describe this agar and its use.
    • Eosin-Methylene Blue Agar
    • Gram Neg selective media like MacConkey, but with different dyes
    • - Uses eosin and methylene blue

    • Lactose Fermenters: turn blue/black, sometimes with a metallic sheen
    • Non-fermenters remain clear
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    Describe this agar and its use.
    Bile-Esculin Agar

    • A medium that contains high [bile salt] and Fe
    • - Inhibits Gram+ organisms
    • - Selects for Enterococcus and Group D Streptococci

    Both hydrolyze esculin, which reacts with the Fe to form the black precipitate
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    Describe this agar.
    Hektoen-Enteric Agar

    • Contains bile salts and indicator dyes like MacConkey
    • Contains lactose, sucrose, and salicin
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    What is this agar used for?
    Hektoen-Enteric Agar

    Selective for Gram Negs (bile and dye inhibit G+)

    • Differential indicators:
    • - Sugar fermentors appear yellow-pink
    • - Non-fermentors appear green or transparent
    • - H2S producers form black precipitate in the colony (e.g. Salmonella)
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    Describe this growth medium.
    • Cetrimide Agar
    • Cetrimide is a detergent that inhibits most bacteria
    • - Selective and differential for Pseudomonas aeruginosa

    • P. aeruginosa produces pyocyanin (blue-green) and fluorescein (yellow-green), which can be visualized
  16. Describe tellurite agar and its use (no picture)
    • A medium with potassium tellurite added to it.
    • - inhibits Gram Neg and most upper respiratory flora

    • It is selective and differential for Cornybacterium diptheriae
    • - Colonies appear gray or black with a brown halo
  17. What are chromogenic agars, and what are they used for?
    Specialized agars selective and differential for various microbes

    Usually differentiate specific species by change in agar color

    e.g. Listeria monocytogenes, S. aureus, or phenotypes like MRSA, MSSA
  18. Define selective media
    A specialized media that selects for the growth of organisms with particular characteristics
  19. Define differential media
    A specialized media that can be used to differentiate particular organisms

    Usually does this by color indicators; does not affect growth patterns (i.e. not inhibitory)
  20. Aerobic vs Anaerobic bacteria
    Aerobic: require O2 for metabolism

    Anaerobic: require reduced O2 tension to grow, increased [CO2]
  21. Simple vs Fastidious
    Simple: organism grows under routine conditions

    Fastidious: organism requires special conditions
Card Set:
Microbiology Growth Media
2011-09-30 01:13:30
semester3 mini1 s3m1 microbiology diagnostic agar growth media med school medical Ross University

Different growth media (agar plates, etc) and growth conditions for microorganisms From Dr. Sloma's "Principles and Strategies of Laboratory Diagnosis"
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