Techniques in Microbiology

Question 1

What is the difference in biosafety level 3 and 4 - give an example of a microbe for each

Answer 1

Manipulations are formed in a safety cabinet
Tuberculosis and Ebola

Question 2

Define a pure culture

Answer 2

A culture containing only a single kind of microbe

Question 3

Equation including magnification

Answer 3

Image size = actual size*magnification

Question 4

Give 2 limitations of microscopic counts

Answer 4

Small cells can be overlooked
Dead and alive cells cannot be distinguished

Question 5

Outline the spread-plate, streak-plate and pour-plate method - what must occur before a spread and pour plate method

Answer 5

Streak - spreading of a mixture using an inoculating loop or swab
Spread - spreading of a mixture using a sterile bent rod
Pour - mixture of sample and liquid agar is incubated
Dilution

Question 6

Give 1 limitation of the pour-plate technique

Answer 6

Hot agar may kill cells

Question 7

What is the great plate count anomaly - give 2 reasons for it

Answer 7

The discrepancy in results between plate counts and microscopy
- Dead cells are counted
- Growth requirements aren’t met

Question 8

Give three ways to measure cell mass - how does the 3rd one work - turbidity?

Answer 8

Dry weight
Concentration of a particular cell constituent
Spectrophotometry - amount of light scattered is directly proportional to cell biomass