lab pt 6

How is the catalase test performed?

Add hydrogen peroxide to bacterial growth on a suitable surface.

What are positive and negative catalase results?

Positive: immediate bubbling from oxygen. Negative: no bubbling.

Why is catalase important to bacteria?

It protects against toxic hydrogen peroxide produced during metabolism.

What is cytochrome oxidase?

An enzyme in certain electron transport chains that transfers electrons to oxygen, the final electron acceptor.

What does a positive oxidase test indicate?

The bacterium possesses cytochrome c oxidase.

How is the oxidase test performed and interpreted?

Apply bacterial growth to oxidase reagent. Rapid dark purple/blue = positive; no rapid color change = negative.

What is urea?

A nitrogen-containing waste compound produced during protein metabolism.

What does urease do and what are its products?

Hydrolyzes urea into ammonia and carbon dioxide.

How does urease affect environmental pH?

Ammonia increases pH, making the environment alkaline.

How is the urease test performed?

Inoculate urea-containing medium and observe the pH indicator.

What are positive and negative urease results?

Positive: pink/fuchsia due to alkaline pH. Negative: original yellow-orange color remains.

What is amylase and what does it do?

An enzyme that breaks starch into smaller carbohydrates by hydrolyzing glycosidic bonds.

How is the starch hydrolysis test performed?

Grow bacteria on starch agar, then flood the plate with iodine.

What does iodine do in the starch hydrolysis test?

It reacts with intact starch, producing a dark blue-black color.

What are positive and negative starch hydrolysis results?

Positive: clear zone around growth. Negative: dark agar remains around growth.

Why does a clear zone indicate amylase activity?

Starch was hydrolyzed and can no longer react with iodine.

What does coagulase do?

Promotes fibrin formation, causing plasma to clot.

Why is coagulase important to bacteria that produce it?

It can help bacteria evade immune defenses by promoting clot formation around them.

Which important bacterium is identified using coagulase testing?

Staphylococcus aureus.

How is the coagulase test performed and interpreted?

Mix bacteria with plasma. Clot/gel formation = positive; liquid plasma = negative.

What is a proteolytic enzyme?

An enzyme that breaks proteins into smaller peptides or amino acids.

What is gelatin?

A protein derived from collagen.

What is gelatinase?

An enzyme that hydrolyzes gelatin into smaller peptides and amino acids.

Why do bacteria produce gelatinase?

To break down proteins and use the resulting nutrients.

How is the gelatin hydrolysis test performed?

Inoculate nutrient gelatin, incubate, and cool the tube before interpreting.

Why must gelatin tubes be cooled before interpretation?

Gelatin liquefies when warm even without bacterial hydrolysis.

What are positive and negative gelatinase results?

Positive: remains liquid after cooling. Negative: solidifies again.

What are casein and caseinase?

Casein is a milk protein; caseinase is an enzyme that breaks it down.

What does a positive casein hydrolysis test look like?

A clear zone around bacterial growth on milk agar.

How do caseinase and gelatinase differ?

Caseinase breaks down casein; gelatinase breaks down gelatin. Both are proteolytic enzymes.