Lab practical 2 review

Is DNase agar selective, differential, or both

Differential

What is the substrate in DNase agar

Polymerized DNA (Deoxyribonucleic Acid)

What is the dye in DNase agar

Methyl green

What ingredients make MSA differential

Mannitol

What ingredients make MSA selective

7.5% NaCl (for halophiles)

What is the pH indicator in MSA

Phenol red

What reaction doe the enzyme catalase catalyze

Breaks down hydrogen peroxide into water and molecular oxygen

How would you perform a catalase test?

Add 2 small drops of 3% hydrogen peroxide onto the slide. Put a loopful of microorganism onto a drop and observe for bubbling

What result would you expect for a staphylococcus species on a catalase test

Positive for catalase

An unknown Gram-positive coccus gives a negative catalase reaction but grows on MSA. What is this organism

Enterococcus faecalis

What is the selective ingredient present in bile agar

Bile salts. Enteric organisms can grow in the presence of bile

What is the differential carbohydrate ingredient present in bile esculin agar

Esculin

What is the differential indicator present in bile esculin

Ferric ammonium citrate

What does MacConkey agar select for

Gram negative bacteria

What ingredients in MacConkey agar make it selective

Crystal violet and bile salts

What are the carbohydrates present in TSI slants? (Triple sugar iron)

Glucose, Sucrose, and Lactose

What is the percentage of glucose in TSI slant

0.1%

What is the percentage of sucrose and lactose in a TSI slant

1.0%

What is the pH indicator in TSI agar

Phenol red

Which components of the TSI slant test for Hydrogen Sulfide production

Sodium thiosulfate acts as the substrate.

Hydrogen Sulfide reacts with ferrous sulfate to create a black precipitate

What is the pH indicator of urea broth (urease test)

Phenol red

Urease breaks down urea into what components?

Ammonia, carbon dioxide, and water

Will the production of urease raise or lower the pH?

Raise the pH, resulting in a hot pink color.

In a SIM tube, hydrogen sulfide production will determine what?

The possession of thiosulfate reductase

In a SIM tube, Indole production will determine what?

The possession of tryptophanase

In a SIM tube, motility will determine what?

Presence of a flagella

What does tryptophanase break tryptophan down into

Indole, pyruvate, and ammonia

What is added to SIM tubes after incubation to test for indole production

Kovac’s reagent (HCl, Butanol and pdaba)

What is the enzyme that catalyzes the production of Hydrogen Sulfide

Thiosulfate reductase

MR and VP tests are an abbreviation of what?

Methyl Red and Vogues-Proskauer

MRVP broth contains what ingredients?

Peptones, Glucose, and Phosphate buffer

The MRVP test was designed to distinguish between which two bacteria?

Escherichia coli and Enterobacter aerogenes

An organism that is positive for the MR test will ferment glucose to produce what?

Lactic, Acetic, and Formic acids

An organism that is positive for the VP test will ferment glucose to produce what?

Only acetic acid, which is then converted to acetoin.

What reagents must be added for the MR test

Methyl Red

What reagents must be added for the VP test

Barritts reagent A and Barritts reagent B

Barritts reagent A is made of what

Alpha naphthol

Barritts reagent B is made of what

40% KOH

Is citrate agar selective, differential or both?

Selective

What enzyme will degrade citrate

Citrase

What is the pH indicator in citrate agar

Bromothymol blue

What is the class of enzymes that reduce nitrate

Nitrate reductase

Do nitrate reductases require oxygen to function?

No, they work as anaerobic

Nitrate is reduced to what?

Nitrite

Nitrite is then converted to what?

Ammonia and/or Nitrogen

What reagents must be added to the nitrate broth tubes after incubation

5 drops of nitrate reagent A, then 5 drops of nitrate reagent B

What does Nitrate reagent A consist of?

Sulfanilic Acid

What does nitrate reagent B consist of

Alpha-Naphthylamine

A red color after adding the reagents signifies what in the nitrate broth?

A positive result, indicating that the nitrate has been reduced to nitrite

A red color after adding zinc to the nitrate broth signifies what?

A negative result, because zinc has reduced the nitrate to nitrite.

If there is NO color change after adding zinc, this will signify what?

A positive result, indicating that nitrate has been reduced to ammonia/molecular nitrogen