Microbio Lab Quiz 7 (More Important to Know)

Microbial Metabolism

Identification of Microorganisms

Identification of microorganisms can be done by microbial biochemical processes that occur when a pure culture is inoculated into media that contains one or more specific substrates. The reactions that can be determined by using indicator reagents

Why is it necessary to have pure cultures when identifying bacteria using biochemical tests?

So that you can get the results you want with no false positives

What is a catalyst?

A substance that speeds up a chemical reaction without being permanently changed by it 

What is an enzyme?

An organic catalyst, often a protein, made by a cell 

Why are enzymes important in activities that occur in cells?

No chemical reactions could occur inside cells without enzymes

Enzymes promote changes only…

in very specific substances or substrates

What ending do many enzymes have?

-ase

What does “anaerobic” mean?

Without oxygen

What are we going to use fluid thioglycolate medium to indicate?

The presence or absence of oxygen

What is a resazurin?

A substance that binds to free oxygen

How will we make a jar anaerobic?

We place a hydrogen generator packet in the jar, along with a catalyst. The hydrogen reacts with the oxygen in the jar

Obligate Anaerobe

• Cannot grow when is O₂ is present

• Is located in the bottom half of the tube in thioglycolate medium

Obligate Aerobe

• Grows only when O₂ is available

• Is located within the red zone at the top of the tube in thioglycolate medium

Facultative Anaerobe

• Grows best when O₂ is available, but also grows without it

• Growth all the way through the tube with the most growth within the red zone at the top of the tube in thioglycolate medium

Aerotolerant Anaerobe 

• Grows equally well with or without O₂ 

• Even growth all the way through the tube in thioglycolate medium 

Microaerophile

• Grows only if small amounts of O₂ are available

• Just below the red zone near the top of the tube in thioglycolate medium

What does the oxidase test tell us about bacteria?

It tells us whether or not the bacteria make oxidase, an enzyme essential for aerobic respiration

Positive Oxidase Test Result

The reagent turns blue/purple within 15 seconds

Negative Oxidase Test Result

Yellow or no color within 15 seconds

Catalase breaks down…

hydrogen peroxide producing oxygen and water

How can we tell if catalase is acting on its substrate?

BUBBLES

Phenol red broth is a differential media. What does a color change in phenol red broth indicate about a bacterium that has been growing in it?

Whether or not the bacterium has the enzymes necessary to ferment the sugar in the tube 

Phenol red broth contains a pH indicator called phenol red, which indicates a pH change when it changes color. State the color of the broth under the following conditions:

• Neutral pH- RED 

• Acidic pH- YELLOW

• Alkaline pH- PINK

What is a Durham Tube and what does it collect?

1. A Durham Tube is a tiny tube that sits upside down in the phenol broth tubes

2. It collects gas

What two products may be produced during fermentation of simple carbohydrates?

Acid and Gas 

How are Acid and Gas identified in the fermentation test? Can you have one without the other?

1. Acid turns phenol red yellow

2. Gas collects in the durham tube so you can see bubbling

3. You can have one without the other

Name 3 simple carbohydrates that can be added to media for biochemical testing

1. Glucose

2. Sucrose

3. Lactose