Lab Exam 2 BIOL 2420 Gram NEGATIVE

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12 Terms

1
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Phenol Red Broths (Dex, Suc, Lac)

Positive: Yellow (acid) ± bubble (gas)
Meaning: Fermentation of the sugar

<p><strong>Positive:</strong> Yellow (acid) ± bubble (gas)<br><strong>Meaning:</strong> Fermentation of the sugar</p>
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MacConkey Agar (MAC)

Positive: Pink colonies (lactose fermenter)
Strong positive: Hot pink precipitate
Meaning: Gram-negative lactose fermentation

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EMB Agar

Positive:

  • Metallic green sheen (strong fermenter)

  • Purple/dark colonies (moderate fermenter)
    Meaning: Lactose fermentation
    Example: E. coli

<p><strong>Positive:</strong></p><ul><li><p>Metallic green sheen (strong fermenter)</p></li><li><p>Purple/dark colonies (moderate fermenter)<br><strong>Meaning:</strong> Lactose fermentation<br><strong>Example:</strong> <em>E. coli</em></p></li></ul><p></p>
4
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Methyl Red (MR)

Positive: Bright red color
Meaning: Mixed-acid fermentation

<p><strong>Positive:</strong> Bright red color<br><strong>Meaning:</strong> Mixed-acid fermentation</p>
5
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Voges-Proskauer (VP)

Positive: Pink/red color after reagents
Meaning: Acetoin (2,3-butanediol pathway)

<p><strong>Positive:</strong> Pink/red color after reagents<br><strong>Meaning:</strong> Acetoin (2,3-butanediol pathway)</p>
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Phenylalanine Deaminase (Phe)

Positive: Green color with FeCl₃
Meaning: Phenylalanine deaminase produced
Examples: Proteus, Morganella, Providencia

<p><strong>Positive:</strong> Green color with FeCl₃<br><strong>Meaning:</strong> Phenylalanine deaminase produced<br><strong>Examples:</strong> <em>Proteus, Morganella, Providencia</em></p>
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Citrate Test

Positive: Blue slant (or growth with blue)

*slant is originally green
Meaning: Citrate used as sole carbon source

<p><strong>Positive:</strong> Blue slant (or growth with blue)</p><p>*slant is originally green<br><strong>Meaning:</strong> Citrate used as sole carbon source</p>
8
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LIA (Lysine Iron Agar)

Positive Reactions:

  • Purple butt → Lysine decarboxylase

  • Red slant → Lysine deamination

  • Black → H₂S

<p><strong>Positive Reactions:</strong></p><ul><li><p><strong>Purple butt</strong> → Lysine decarboxylase</p></li><li><p><strong>Red slant</strong> → Lysine deamination</p></li><li><p><strong>Black</strong> → H₂S</p></li></ul><p></p>
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Urea Broth

Positive: Hot pink (fuchsia)
Meaning: Urease enzyme active

10
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TSI (Triple Sugar Iron)

Positive Indicators:

  • A/A (yellow slant & butt) → glucose + lactose/sucrose fermentation

  • K/A (red slant, yellow butt) → glucose only

  • Black → H₂S

  • Bubbles/cracks → gas

<p><strong>Positive Indicators:</strong></p><ul><li><p><strong>A/A (yellow slant &amp; butt)</strong> → glucose + lactose/sucrose fermentation</p></li><li><p><strong>K/A (red slant, yellow butt)</strong> → glucose only</p></li><li><p><strong>Black</strong> → H₂S</p></li><li><p><strong>Bubbles/cracks</strong> → gas</p></li></ul><p></p>
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MIO (Motility, Indole, Ornithine)

Motility Positive: Cloudy growth beyond stab
Indole Positive: Red ring with Kovac’s reagent
Ornithine Positive: Tube turns purple

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Oxidase Test

Positive: Dark purple within 30 sec
Meaning: Cytochrome c oxidase present
Examples: Pseudomonas, Neisseria

<p><strong>Positive:</strong> Dark purple within 30 sec<br><strong>Meaning:</strong> Cytochrome c oxidase present<br><strong>Examples:</strong> <em>Pseudomonas, Neisseria</em></p>