Module 4

Question 1

True or False: Differential media is best suited for distinguishing between two similar species of bacteria

Answer 1

True

Question 2

A researcher is asked to determine which of two vials contains E coli and which contains salmonella. Knowing both are Gram-negative while only one of them is capable of fermenting lactose, which type of media would be best suited?

Answer 2

Differential Media

Question 3

What are the requirements of a fastidious microbe?

Answer 3

A fastidious microbe requires specific and often complex nutritional and environmental conditions to grow and thrive.

Question 4

True or False: LB agar is classified as a selective, non-differential media.

Answer 4

F

Question 5

The polysaccharide-based hardening agent added to LB media to produce LB agar is derived from what?

Answer 5

Seaweed (algae) extract.

Question 6

Blood agar is which type of medium? Select all that apply.

Selective
Enriched
Selective and Differential
Differential

Answer 6

Enriched
Differential

Question 7

Match the following hemolytic class with its description of activity.

1. Alpha hemolysis A. No change.
2. Beta hemolysis B. Greenish-brown color
3. Gamma hemolysis C. Distinct zone of clearing

Answer 7

1. Alpha hemolysis –> B. Greenish-brown color
2. Beta hemolysis —> C. Distinct zone of clearing
3. Gamma hemolysis –> A. No change.

Question 8

Columbia CNA agar is most closely related to which media:

Answer 8

Blood agar

CNA agar is similar to BAP as it is also enriched with blood and allows for differentiation based on hemolytic patterns.

Question 9

True or False: Chocolate agar gets its brown color from cocoa to produce an enriched media.

Answer 9

F

Question 10

An unknown microbe is streaked onto a MacConkey agar plate. After an overnight incubation at 37°C, growth is observed. Would a Gram stain be necessary? Why or why not?

Answer 10

No. A Gram stain would not be necessary, as only Gram-Negative microbes will grow on MacConkey agar.

Question 11

In Eosin Methylene Blue (EMB) agar, what color indicates the presence of E. coli?

Answer 11

metallic green

Question 12

Which type of agar media is best suited to support the growth of Staphylococcus?

Answer 12

Mannitol salt agar

Question 13

What is the process of spreading a bacterial culture onto a petri dish called?

Answer 13

Plating

Question 14

Describe the primary advantage of using a petri dish over growing a liquid culture?

Answer 14

Using a petri dish allows for the microbes to be held in place and be easier controlled in terms of isolation.

Question 15

True or False: The visualization of colonies on a petri dish represents bacterial cells that have multiplied ~2-3 times.

Answer 15

F

Question 16

True or False. The purpose of a quadrant streak is to expand a bacterial population.

Answer 16

F

Question 17

Which of the following are correct in order to be considered a pure culture? Select all that apply.

Single organism
Multiple species
Obtained by a serial dilution method
Obtained by pour plate serial dilution method
Obtained by a 4-phase dilution streak method
Long lifespan
Free from contaminants

Answer 17

Single organism
Obtained by a serial dilution method
Obtained by pour plate serial dilution method
Obtained by a 4-phase dilution streak method
Free from contaminants

Question 18

A dilution gradient is formed when carrying out what generalize plating strategy?

Answer 18

A quadrant streak

Question 19

In what phase of a dilution streak would you expect to find the lowest concentration of bacteria, P2 or P4?

Answer 19

P4 (Phase 4) would contain the lowest concentration of bacteria. The phases rank (from highest to lowest), P1 > P2 > P3 > P4.

Question 20

True or False. When performing a dilution streak a new (or sterilized) loop is not required for each phase as long as the bacterial culture is pure.

Answer 20

False

Question 21

What might a researcher do when performing a phase dilution streak to encourage growth of single colonies if starting from a highly concentrated culture?

Answer 21

Increase the number of dilution phases on the plate

Question 22

True or False. Pathogenic strains of bacteria tend to grow slower than normal non-pathogenic bacterial strains.

Answer 22

F

Question 23

When given an unknown bacterial sample the first step is to expand the current bacterial population. Which form of media best suites this need? Why?

MSA agar
LB media
MacConkey agar
Columbia CNA agar

Answer 23

LB media, because this type of media is non-selective and non-differential.

Question 24

What is another name for a liquid growth media, what are the basic components?

Answer 24

Nutrient broth. The basic components are sugar, amino acids, and vitamins.

Question 25

In an attempt to detect the presence of the pathogenic strain of E. coli O157:H7, a researcher spread a culture onto a MacConkey agar with failed results. What type of agar should they (correctly) try next? Based upon what you know about the formulation of differential plates, explain why you chose this specific agar.

Answer 25

To detect E. coli O157, the researcher should use MacConkey Sorbitol agar. This agar differentiates E. coli O157 from other E. coli strains by its inability to ferment sorbitol, resulting in colorless colonies compared to pink colonies of sorbitol-fermenting strains.

Question 26

A researcher is asked to determine if a sample contains Neisseria meningitides. Knowing Neisseria meningitides is slow growing and other foreign microbes may also be present in the culture, which type of media would be best suited? Growth Media Selective Media Selective and Differential Media Differential Media

Answer 26

Selective Media

Question 27

What is the Gram status (positive or negative) of microbes growing on Eosin Methylene Blue (EMB) agar plates?

Answer 27

Gram-negative

Question 28

Which type of agar media is best suited to support the growth of Staphylococcus? Columbia CNA agar Blood agar Chocolate agar Mannitol salt agar MacConkey agar

Answer 28

Mannitol Salt Agar

Question 29

What is agar used for in microbiology?

Answer 29

Its used to create a solid and smooth surface so microbes can grow on

Question 30

Mannitrol salt agar will turn what color in the presence of the pathogenic strain staphylococcus aureus.

Answer 30

Yellow

Question 31

What is the process of spreading a bacterial culture onto a petri dish?

Answer 31

Plating

Question 32

In order to visual individual colonies of bacteria would you culture your sample in a liquid media or on a solid (agar) media? Why?

Answer 32

Solid Agar. Because the liquid media is where bacterial cells can multiply but are able to move around in the solution; whereas, bacteria plated on a solid agar are fixed and support the formation and visualization of colonies.

Question 33

True or False: The visualization of colonies on a petri dish represents bacterial cells that have often multiplied a million times over.

Answer 33

True

Question 34

True or False. The purpose of a quadrant streak is to produce individual colonies of a bacterial population.

Answer 34

True

Question 35

True or False: The purpose of the quadrant streak is to expand bacterial population

Answer 35

False

Question 36

To be considered a pure culture, the sample (1) ______(2)__________ ?

Answer 36

Traced back to a single cell and not have any contaminents

Question 37

In what phase of a dilution streak would you expect to find the lowest concentration of bacteria, P2 or P4?

Answer 37

P4

Question 38

In order to encourage growth of a slow growing microbe what might a researcher do during a phase dilution streak?

Answer 38

A researcher could either choose to involve fewer phases (3 phases instead of 4) or pass the loop through the previous phase numerous times (instead of only once).

Question 39

True or False. Pathogenic strains of bacteria tend to grow slower than normal non-pathogenic bacterial strains.

Answer 39

F

Question 40

True or False; To restrict growth of a pathogenic microbe a researcher might decrease an incubator from 37 to 25C

Answer 40

T

Question 41

When given an unknown bacterial sample the first step is to expand the current bacterial population. Which form of media best suites this need? Why? 1) MSA agar 2) LB media 3) MacConkey agar 4) Columbia CNA agar

Answer 41

LB Media