Culturing Microorganisms In The Laboratory

Question 1

How do you investigate microorganisms for the diagnosis of disease or for scientific experiemnt?

Answer 1

Culture them
Growing large enough numbers of the microorganisms for us to see them with the naked eye

Question 2

Why must health and safety be used when culturing microorganisms, even if they are harmless?

Answer 2

Risk of mutation making strain pathogenic

May be contamination with pathogenic microorganisms from the environment

Question 3

What do microorganisms need to be cultured?

Answer 3

Food= nutrient medium- liquid form (broth) or solid (agar)
Nutrients added to medium- protein- blood, yeast extract or meat
Medium must be kept sterile- aseptic techniques

Right conditions- temperature, oxygen, PH

Question 4

What is inoculation?

Answer 4

Once agar or broth prepared, bacteria is added by inoculation

Question 5

What is the process of broth inoculation?

Answer 5

1. Make suspension of bacteria to be grown
2. Mix known volume with sterile nutrient broth in flask
3. Stopper flask with cotton wool to prevent contamination from air
4. Incubate at suitable temp, shake regularly aerate providing oxygen for bacteria growth

Question 6

How is agar inoculated?

Answer 6

1. Wire inoculating loop sterilised by flaming until it glows, don’t let it touch any surfaces
2. Dip loop in bacterial suspension, remove lid of Petri dish, make zig-zag streak across agar surface, surface of agar must be kept intact
3. Replace lid of Petri dish, tape down, not sealed completely so oxygen can enter preventing growth of anaerobic bacteria

Question 7

What acts as a break on reproduction and growth in a closed system?

Answer 7

Limited nutrients

Build up of waste

Question 8

What is used to represent the bacterial population?

Answer 8

Logarithmic numbers (log)

As difference in numbers from initial population to final population can be too great to represent using standard numbers

Question 9

What are the different stages of a graph showing bacteria growth!

Answer 9

Lag phase- bacteria adapting to new environment- growing, synthesising enzymes they need and not yet reproducing at max rate

Log/exponential phase- rate of reproduction is close to or at its theoretical max

Stationary phase- net growth = 0, number of cells formed by binary fusion is cancelled out by number of cells dying

Decline/death phase- reproduction has almost ceased, death rate of cells increasing

Question 10

Which limiting factors prevent continuous exponential growth of bacteria?

Answer 10

Nutrients available- nutrient level will become insufficient to support number of replication

Oxygen levels- as pop rises, so does demand for respiratory oxygen, oxygen levels can become limiting

Temperature- enzyme-controlled reactions within microorganisms affected by temp of culture medium

Build-up of waste- as bacterial numbers increase, build up of toxic material may limit further growth, can poison and kill culture

Change in PH- as carbon dioxide produced by respiration of bacterial cells increases, PH of culture falls until a point where the low PH affects enzyme activity and inhibits pop growth