Microbiology Agar Quiz

What is Mannitol Salt Agar (MSA) Selective for?

Halophile Bacteria

What is Mannitol Salt Agar (MSA) Differential For?

Distinguishes Bacteria that ferment mannitol.

White, meaning it doesn’t ferment mannitol, and yellow, meaning it does ferment mannitol

What is MacConkey Agar (MAC) Selective for?

Gram Negative Bacteria (MAC)

What is MacConkey Agar (MAC) Composed of?

Crystal Violet and Bile Salts (Bile Salts inhibit the growth of Gram-Positive Bacteria)

What does MacConkey Agar (MAC) tell us?

Colorless means it doesn’t ferment lactose, Pink means it does ferment lactose.

What does a Catalase Test show us?

Presence of catalase enzyme, bubbles indicating the presence of catalase

What does Bile Esculin Agar (BILE) selective for?

Inhibits Gram-Negative with the help of Sodium Azeride and Bile salts to inhibit some Gram-Positive Bacteria

What makes Bile Esculin Agar (BILE) tell us?

growth = Gram-Positive Bacteria

Black = Hydrolyzes Esculin 

What is Eosin and Methylene Blue Agar (EMB) selective towards?

Selective towards Gram-Negative Bacteria (EMB)

What in EMB plates makes it inhibit Gram-Positive Bacteria?

Eosin y and Methylene Blue

What does an EMB plate show us?

Lactose Fermentation Rate

Colorless = Doesn’t Ferment

Pink/Brown = Slow Fermentation

Black/ Green sheen = Vigorous Fermentation

What does the Coagulase Test, test for?

For the enzyme Coagulase, which clots blood.

Clumps = Positive 

How is Blood Agar Differential?

Based on the Types of Hemolysis

What is a Gamma Result on a Blood Agar?

White - NO Hemolysis

What is a Beta Result on a Blood Agar?

Clear - COMPLETE Hemolysis

What is a Alpha Result on a Blood Agar?

Green/Brown - PARTIAL Hemolysis

What is a Hektoen Enteric Agar (HEK) selective for?

Selective towards Gram-negative bacteria due to the Bile salts present that inhibit Gram-positive bacteria

On a Hektoen Enteric Agar, what does a Colorless result mean?

No Fermentation is Present

On a Hektoen Enteric Agar, what does a Black result mean?

Hydrogen Sulfide Production

On a Hektoen Enteric Agar, what does an Orange/Yellow result mean?

The Bacteria present ferment either Lactose, Sucrose or Salicin 

What does an Oxidase Test, test for?

Test for the Presence of Cytochrome enzyme

Purple = Positive

How is a Citrate Test Differential?

Shows whether a bacterium can use citrate as a carbon source

Colorless/Green = Doesn’t Use Citrate

Blue = Uses Carbon as a Carbon Source

How is Triple Sugar Iron Agar (TSI) Differential?

Because it distinguishes bacteria based on their ability to ferment Lactose, Sucrose, and Glucose, produce gas, and generate hydrogen sulfide. and showing oxygen tolerance

On a TSI what does a Red/Red tell us?

NO Fermentation Occured

On a TSI, what does red/yellow tell us?

glucose fermentation is present

On a TSI, what does a yellow/yellow tell us?

Lactose and or Sucrose Fermentation

On a TSI, what does a Split Agar Tell us?

Gas was Produced

Ona TSI, what does black mean?

Hydrogen Sulfide was produced 

What does a Motility Test, test for?

Presence of a Flagella

Fuzzy + Red throughout = Positive