Question 1

Which of the following best describes a pure (axenic) culture in microbiology?

Accepted Answer

A culture containing only one species, strain, or variety of microorganism.

Question 2

Why is it essential to use aseptic techniques when performing streak plate or pour plate methods?

Accepted Answer

To prevent contamination and ensure the isolation of pure cultures.

Question 3

Which of the following is a key advantage of the streak plate method over the pour plate method?

Accepted Answer

It does not require prior dilution of the inoculum.

Question 4

A student is trying to isolate a strict aerobe from a mixed culture. Which technique should they use and why?

Accepted Answer

Streak plate, because strict aerobes grow best on the surface where oxygen is available.

Question 5

Which of the following steps is NOT part of the streak plate method for isolating colonies?

Accepted Answer

Pouring melted agar over the inoculum.

Question 6

In the pour plate method, why is it important to use agar cooled to approximately $$55^{\circ}C$ before pouring?

Accepted Answer

To avoid killing the microorganisms with excessive heat.

Question 7

Which type of microorganism is most likely to be favored by the pour plate method?

Accepted Answer

Anaerobic facultative microorganisms.

Question 8

A researcher wants to count the number of viable bacteria in a water sample. Which method should they use and why?

Accepted Answer

Pour plate, because it distributes bacteria throughout the agar and allows for accurate colony counts.

Question 9

Which of the following best explains why the streak plate method is considered a standard technique in clinical and research laboratories?

Accepted Answer

It is simple, reproducible, and requires minimal sample volume.

Question 10

During the streak plate method, why is it important to flame the inoculating loop between streaking each quadrant?

Accepted Answer

To sterilize the loop and reduce the number of microorganisms transferred, leading to isolated colonies.

Question 11

Which of the following scenarios would most likely result in a mixed culture rather than a pure culture?

Accepted Answer

Not flaming the inoculating loop between streaks and picking multiple colonies for subculture.

Question 12

A student observes that after performing a pour plate, colonies are present both on the surface and within the agar. What does this indicate?

Accepted Answer

The pour plate method allows for the growth of both surface and subsurface colonies.

Question 13

Which piece of equipment is essential for transferring microorganisms during the streak plate method?

Accepted Answer

Inoculating loop.

Question 14

What is the main reason for incubating Petri dishes in an inverted position after inoculation?

Accepted Answer

To prevent condensation from dripping onto the agar surface.

Question 15

Which of the following best describes a bacterial colony?

Accepted Answer

A visible aggregation of cells derived from a single microorganism.

Question 16

If a student fails to flame the mouth of the culture tube before and after inserting the inoculating loop, what is the most likely consequence?

Accepted Answer

The culture may become contaminated with airborne microorganisms.

Question 17

Which of the following equations best represents the calculation for colony-forming units (CFU) per mL in a pour plate experiment?

Accepted Answer

$$	ext{CFU/mL} = \frac{	ext{Number of colonies}}{	ext{Dilution factor} 	imes 	ext{Volume plated (mL)}}$$

Question 18

Which historical figure is credited with developing the original pure culture technique?

Accepted Answer

Robert Koch

Question 19

A laboratory is attempting to isolate a microorganism that grows best in low-oxygen environments. Which method should they use and why?

Accepted Answer

Pour plate, because it creates microenvironments with lower oxygen concentrations within the agar.

Cultivo Puro: Técnicas de Estriado y Vertido en Placa

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