MICRO LAB- Biochemistry of Gram Positives

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Last updated 2:54 PM on 6/17/26
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9 Terms

1
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Mannitol Salt Agar

Selective and Differentual

  • selective agents: 7.5% NaCl (table salt) selects for Staphylococcus bacteria

  • Differential Agents: Phenol Red turns yellow under acidic conditions

Mannitol ————→ Acid end products

Mannitol Salt Agar

  • Medium: Mannitol Salt Agar

  • Substrate: Mannitol

  • Enzyme: N/A

  • Other reagents: Selective agent (7.5% NaCl), Differential agent (Phenol Red pH indicator)

<p>Selective and Differentual</p><ul><li><p>selective agents: 7.5% NaCl (table salt) selects for Staphylococcus bacteria</p></li><li><p>Differential Agents: Phenol Red turns yellow under acidic conditions</p></li></ul><p><strong>Mannitol ————→ Acid end products</strong></p><p><strong>Mannitol Salt Agar</strong></p><ul><li><p><strong>Medium</strong>: Mannitol Salt Agar</p></li><li><p><strong>Substrate: </strong>Mannitol</p></li><li><p><strong>Enzyme: </strong>N/A</p></li><li><p><strong>Other reagents: </strong>Selective agent (7.5% NaCl), Differential agent (Phenol Red pH indicator)</p></li></ul><p></p>
2
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Catalase Test

2 H2O2 —————-(Catalase)———> 2H2O + O2

Catalase is an enzyme that breaks down hydrogen peroxide into water and oxygen. The presence of oxygen bubbles indicates a positive result. This test must be conducted using specimens from a plate or slant, and not from a broth

<p><strong>2 H2O2 —————-(Catalase)———&gt; 2H2O + O2</strong></p><p>Catalase is an enzyme that breaks down hydrogen peroxide into water and oxygen. The presence of oxygen bubbles indicates a positive result. This test must be conducted using specimens from a plate or slant, and not from a broth</p><p></p>
3
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Blood Agar

Differential for types of hemolysis

  • blood plates must be streaked for isolation, and hemolysis must be rad at isolated colonies by holding the plate up to the light and looking for changes to the medium and around isolated colonies

Gamma (No) Hemolysis:

  • No change to the red color of the blood medium around isolated colonies

Alpha (Partial) Hemolysis:

  • partial change to red color of blood medium around isolated colonies, indicating incomplete hemolysis

Beta (Complete) Hemolysis

  • complete clearing of the red color of blood medium around isolated colonies, indicating complete hemolysis

<p>Differential for types of hemolysis</p><ul><li><p>blood plates must be streaked for isolation, and hemolysis must be rad at isolated colonies by holding the plate up to the light and looking for changes to the medium and around isolated colonies</p></li></ul><p>Gamma (No) Hemolysis:</p><ul><li><p>No change to the red color of the blood medium around isolated colonies</p></li></ul><p>Alpha (Partial) Hemolysis:</p><ul><li><p>partial change to red color of blood medium around isolated colonies, indicating incomplete hemolysis</p></li></ul><p>Beta (Complete) Hemolysis</p><ul><li><p>complete clearing of the red color of blood medium around isolated colonies, indicating complete hemolysis</p></li></ul><p></p>
4
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How many organisms will you streak on an individual blood agar plate?

1

5
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What are two important things to remember when obtaining an inoculum to do a catalase test? (Select the two that apply)

You should never take samples for this test from a medium that contains blood.

You need many cells, so samples must come from a solid medium, such as a plate or slant

6
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What are important things to remember when reading the results of a hemolysis test? (Select all that apply)

There are three possible hemolysis results

Read only around isolated colonies

Read the change in the media, not in the bacteria

7
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The selective reagent in Mannitol salt agar is

table salt (NaCl)

8
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How many organisms will you use to inoculate the mannitol salt agar plate?

3

9
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You obtain your mannitol salt agar plate after it has incubated for 2 days. One of the species did not grow. Select the correct results for this from the options below.

Growth negative; Mannitol???

If the organism did not grow, you have no way of knowing whether it is capable of using the mannitol in the medium.