Microbiology Lab Quiz 3

Front 1

What is the purpose of Mannitol Salt Agar (MSA)?

Back 1

To isolate and differentiate pathogenic strains of staphylococci, particularly Staphylococci aureus.

Front 2

What parts of the Mannitol Salt Agar (MSA) plate makes it

a) selective for the growth of both regular Staphylococcus and

b) selective for the growth of pathogenic species of Staphylococcus??

Back 2

a) The sodium chloride makes it selective for growth of Staphylococcus, since most other species of bacteria can't survive this level of salinity.

b) Pathogenic species of Staphylococcus are capable of fermenting mannitol.

Front 3

For Mannitol Salt Agar (MSA), how can you tell if the growth you see is from Pathogenic strains of Staphylococcus versus nonpathogenic strains?

Back 3

Since pathogenic strains ferment mannitol, they produce acid, which will turn the plate yellow.

Nonpathogenic strains will grow on the plate but won't change the color.

Front 4

If the MSA plate turns yellow, does that automatically mean the bacteria that grew is S. aureus?

Back 4

NO, but it's likely, since S. aureus produces most staph infections. However, it is possible that it's a different pathogenic strain.

Front 5

What is a catalase test used for?

Back 5

To identify organisms that produce the enzyme catalase.

Front 6

How does a catalase test work?

Back 6

-You take live bacteria on slides and you drip hydrogen peroxide (H2O2) onto the slides.

-Bacteria that don't produce catalase will be killed by the H2O2 and therefore you won't notice anything after pouring on the H2O2.

-Bacteria that are catalase-positive are immune to H2O2 and convert it via catalase to O2 and H2O. On this plate, you'll immediately see bubbling as O2 forms.

Front 7

What is blood agar used for?

Back 7

For the isolation and cultivation of many kind of fastidious bacteria. Also used to differentiate bacteria based on their hemolytic abilities.

Front 8

What are hemolysins?

Back 8

exotoxins produced by gram-positive bacteria that can destroy red blood cells and hemoglobin.

Front 9

What are the 3 different types of hemolysis?

Back 9

1) alpha-hemolysis: partial hemolysis

2) Beta-hemolysis: complete hemolysis

3) gamma-hemolysis: no hemolysis

Front 10

When observing growth on a blood agar plate, how can you tell the difference between alpha, Beta and gamma hemolysis?

Back 10

1) alpha-hemolysis: greenish color on agar

2) Beta-hemolysis: clearing of the agar on the plate around the colonies/agar looks clear.

3) gamma-hemolysis: simple growth with no color change on the plate. (Growth usually looks white)

Front 11

What are the 2 different enzymes used in Beta-hemolysis by Streptococcus pylorins?

Back 11

1) Streptolysin S = oxygen-stable

2) streptolysin O = oxygen-sensitive

Front 12

When testing the effectiveness of an antimicrobial on bacterial growth, you divide the TSA plate up into multiple sections that will be streaked after a certain time interval has passed with a mixture of the antimicrobial and the microbe in question. What is the purpose of streaking the sector marked "0 minutes"?

Back 12

This is your control: it's used to see if you did the experiment correctly.

Front 13

What is the Zone of Inhibition? What does its size tell you?

Back 13

The Zone of Inhibition is the clear zone that will appear around the site where the antimicrobial agent was added. The bigger the zone is, the more sensitive the bacteria are to that antimicrobial agent.

Front 14

True or false: adding heat usually increases the effectiveness of an antimicrobial agent?

Back 14

TRUE

Front 15

What effect do endospore production capability and time have on a bacteria's ability to survive an antimicrobial?

Back 15

-Endospore production ability = bacteria is more likely to survive.

-leaving the antimicrobial agent on the bacteria for an increased amount of time = the bacteria is less likely to survive.

Front 16

What is GFP?

Back 16

Green Fluorescent Protein: when expressed (when the GFP gene is present and activated), it will cause the organism to glow green under UV light.

Front 17

What must be present for the GFP gene to be activated/expressed on a bacterium?

Back 17

Arabinose. If present, it'll bind to protein AraC (which is always expressed), and this complex will then in turn binds to the promoter region for the GFP gene.

Front 18

What does the beta-lactamase gene do? Why is it known as a Selectable Marker?

Back 18

Codes for the enzyme that breaks down the antibiotic ampicillin,

Known as a selectable marker because it tells us which cells have been transformed to be able to grow in the presence of antibiotic.

Front 19

What is the pGLO plasmid?

Back 19

An engineered plasmid known for containing both the genes to produce GFP as well as the gene to make beta-lactamase (AKA the ampicillin-resistance gene).

Front 20

What would you expect to see on a bacterial culture where there was no ampicillin present and no pGLO plasmid added?

Back 20

-You'd see growth

-But you wouldn't see fluorescence because the GFP protein isn't here.

Front 21

What would you expect to see on a bacterial culture where there was no pGLO plasmid added but there was ampicillin added?

Back 21

-No bacterial growth due to the antibiotic

Front 22

What would you expect to see on a bacterial culture wherein you added both ampicillin AND the pGLO plasmid, but no arabinose?

Back 22

You would see growth despite the ampicillin because the plasmid added contains the gene for the enzyme needed to neutralize ampicillin (beta-lactamase).

-you wouldn't see fluorescence because there's no arabinose

Front 23

What would you expect to see on a bacterial culture wherein you added Ampicillin, the pGLO plasmid, AND arabinose?

Back 23

-You'd see bacterial growth because the pGLO plasmid has DNA to break down ampicillin

-you would see fluorescence because arabinose is present, meaning the GFP protein present can glow.