Cultivation of bacteria

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4. Identification of Unknown Bacteria


  1. Define:

    1. Selective medium- Give examples.

    2. MAC agar

  2. Mannitol salt agar

Eosin methylene blue agar

  1. Differential medium- Give examples.

  2. MAC agar

Blood agar

Mannitol salt agar

Eosin methylene blue agar

2. MacConkey (MAC) Agar


  • MacConkey agar selects for which group of bacteria? Explain.

  • Gram negative

MacConkey agar media differentiates between enteric bacteria based on what biochemical reaction? Explain.

Lactose or lactase

Fermentation of lactose

If the organism is E.Coli, what would you see on your plates? Explain.

  • The plate will have substantial growth with a color change that is pink but instead of just the bacteria growth being pink, the surrounding area is also a pink color

pink

If the organism(s) is/are other enterics, what would you see on your plate? Explain.

  • There would be growth on the plate, but the color change would be able to tell the difference between lactose positive and negative bacteria.

Red/tan

3. Eosin methylene blue (EMB) Agar

    • A nutrient medium that is both selective and differential; it selects for the growth of Gram- negative bacteria and against the growth of Gram-positive bacteria and differentiates Gram-negative bacteria based on the ability to ferment lactose.

  • If the organism is E.Coli, what would you see on your plates? Explain.

  • a metallic green sheen

Eosin methylene blue (EMB) Agar

  • EMB agar selects for which group of bacteria? Explain.

  • Gram negative

EMB agar media differentiates between gram negative enterics based on what biochemical reaction? Explain.

Fermentation of lactose

If the organism(s) is/are other enterics, what would you see on your plate? Explain.

  • No growth for positive and green sheen for multiple types of lactose breakdown.  Regular blue to for normal fermenters

4. Mannitol salt agar (MSA)

  • If the organism is Staphylococcus aureus, what would you see on your plates? Explain.

  • able to ferment mannitol and turns the media yellow.

If the organism is other Staphylococcus epidermis, what would you see on your plate? Explain.

does not ferment mannitol, so the medium remains pink.

5. Mannitol salt agar (MSA)

  • MSA agar selects for which group of bacteria? Explain.

  • staphlococci

MSA agar media differentiates staphylococcal species based on what biochemical reaction? Explain.

  • Fermenting mannitol

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