Microbiology

Question 1

What are aseptic techniques?

Answer 1

A range of techniques used to culture microorganisms under sterile conditions in order to minimize contamination.

Question 2

List the basic aseptic techniques

Answer 2

-Wipe surfaces with antibacterial cleaner
-Set up Bunsen burner nearby
-Flame inoculating loop and neck of bottles before use
-Minimize time that vessels containing bacteria are open
-Sterilize all equipment
-Wear protective clothing

Question 3

Outline how to culture microorganisms

Answer 3

-transfer bacteria to an agar plate using a sterile. inoculating loop or pipette
-tape on lid at two ends, invert dish and incubate.
-In the lab, ensure dish isn’t airtight and do not incubate above 25°C to avoid growth of pathogens.

Question 4

How should you sterilize an inoculating loop?

Answer 4

Pass it through a blue Bunsen burner flame

Question 5

What are inoculating loops used for?

Answer 5

To transfer microorganisms

Question 6

What is an autoclave?

Answer 6

A machine that uses hot steam to sterilize equipment.

Question 7

Why are microorganisms not cultured at temperatures above 25°C in schools?

Answer 7

To avoid the growth of pathogens that are harmful to humans

Question 8

Why should you place a lid on an agar plate?

Answer 8

To prevent microorganisms from the air from contaminating it and to prevent the culture contaminating other areas.

Question 9

Give 4 safety precautions to take when culturing microorganisms

Answer 9

wear protective equipment, wash hands before and after, keep eyes and face away from the culture medium and clean all work surfaces.

Question 10

What is dilution plating?

Answer 10

Using serial dilutions to produce dilute cell cultures from an original sample. This allows the number of microorganisms to be counted and quantified.

Question 11

What is a serial dilution?

Answer 11

A sequence of dilutions (in which the dilution factor is constant) is used to dilute a stock solution. This can be used to dilute cultures for dilution plating

Question 12

What is microbiological turbidity?

Answer 12

The cloudiness of a solution which is based on the amount of microorganisms in a solution and can be measured quantitatively to analyze microbial growth.

Question 13

How can microbiological turbidity be measured?

Answer 13

By passing light through a sample and measuring how much has been absorbed by the sample using a detector on the other side of the sample.

Question 14

What is a hemocytometer?

Answer 14

Glass microscope slide with a grid divided into 9 squares, each 1mm2. Central area for counting contains 25 large squares, each divided into 19 smaller squares.

Question 15

How can the number of original bacteria be estimated from the number of colonies present?

Answer 15

Each bacteria will divide many times to produce a single colony. The amount of colonies should be equal to the number of original bacteria.

Question 16

Why is counting colonies an inaccurate method of determining the original number of bacteria?

Answer 16

-Colonies may clump together
-Often there will be lots of colonies so counting may be difficult.

Question 17

Name the 4 phases of a bacterial growth curve

Answer 17

1. lag phase
2. log phase
3. stationary phase
4. death phase

Question 18

What happens during the lag phase?

Answer 18

Microorganisms need time to adjust to the environment before reproducing so population size only increases slowly.

Question 19

What happens during the log phase?

Answer 19

After every round of division, population size doubles (exponential growth)

Question 20

What happens during the stationary phase?

Answer 20

Reproduction rate = death rate, so population size establishes at its maximum.

Question 21

What happens during the death phase?

Answer 21

Microorganisms die due to buildup of toxic waste products and lack of nutrients.

Question 22

What is the formula needed to calculate the amount of microorganisms in a sample during the exponential growth phase?

Answer 22

Number of organisms = 2^(number of generations)

Question 23

How is the doubling time of a bacterial colony in the exponential growth phase calculated?

Answer 23

Doubling time = total time in exponential phase / number of generations