Fundamental Skills for Microbiology Lab

Question 1

What is a microbial culture?

Answer 1

A medium that contains living microbes

Question 2

What is a pure culture?

Answer 2

A culture that contains a single species

Question 3

What does the term ‘aseptic’ or ‘aseptically’ mean?

Answer 3

Transfer microbes from their pure culture to a sterile medium without disease / contamination

Question 4

What does it mean to ‘culture’ a microorganism?

Answer 4

A sample (inoculum) is introduced to a collection of nutrients (medium)

Question 5

What is an inoculum?

Answer 5

The source material / sample used for inoculation

Question 6

What is a medium in the context of culturing microorganisms?

Answer 6

A liquid / gel designed to support the growth of microorganisms

Question 7

What is a microbial colony?

Answer 7

A culture that is visible on the surface of solid media

Question 8

What must be done to inoculating instruments to prevent contamination?

Answer 8

Instruments are sterilized immediately before use in a bunsen burner flame

Question 9

Differentiate between inoculating loops and inoculating needles

Answer 9

• Inoculating loops are used to retrieve liquid media
• Inoculating needles are used to retrieve solid / dense media

Question 10

What special precautions should be taken with tubes or flasks (specifically the ‘necks’ of these items) to insure aseptic technique is successful?

Answer 10

The mouths / tubes or flasks containing cultures are also incinerated at the time of transfer by passing their opening through a flame

Question 11

Differentiate between transfer pipettes and pasteur pipettes

Answer 11

• Transfer pipettes have a rubber bulb
• Pasteur pipettes have a glass bulb

Question 12

How must a tube culture, or any tubed-samples, be held?

Answer 12

By the tube - not the cap

Question 13

How should the inoculating instrument be held?

Answer 13

Like a pencil - in the dominant hand

Question 14

How should the Bunsen burner be adjusted for proper use?

Answer 14

Adjust the bunsen burner so the flame has an inner and outer cone

Question 15

What is a mixed culture?

Answer 15

A microbial culture consisting of 2 or more species

Question 16

What is the most commonly used isolation technique in microbiology?

Answer 16

The streak plate method

Question 17

What is the goal of any streak plate isolation method?

Answer 17

To obtain isolated colonies from an inoculum by creating areas of increasing dilution on a single plate

Question 18

Is the quadrant streak plate method most applicable to cultures having a high or low initial cell density?

Answer 18

High cell density

Question 19

What tool is used in the streak plate method?

Answer 19

An inoculating loop

Question 20

Differentiate between ‘colonies’ and ‘colony-forming units’ (CFUs)

Answer 20

• Colonies are groups of bacteria that grew from an original bacterium
• Colony-forming units measure viable cells

Question 21

Describe serial dilution (2)

Answer 21

• A series of dilutions in which the dilution factor remains the same for each step
• Allows estimation of a sample’s concentration

Question 22

Describe how the spread plate method of isolation is performed

Answer 22

A method of isolation in which diluted microbial sample is deposited on an agar plate and spread uniformly across the surface

Question 23

What tool is used in the spread plate method?

Answer 23

A glass rod