Culturing Microorganisms- GCSE Biology Practicals

How are microorganisms cultured in the lab?

they are grown in a 'culture median'

what do microorganisms need to grow?

carbohydrates, minerals, proteins and vitamins

What can culture medians be?

nutrient broth solution or solid agar jelly

Rules

Don't keep above 25c because harmful pathogens are more likely to grow above this

what will bacteria form on agar plates

visible colonies on the jelly surface or spread out to give even covering

How to culture microorganisms

1. make an agar plate by placing hot agar jelly into petri dishes

2. when jelly cools and sets, use inoculating loops to transfer microorganism to the median culture

3. alternatively a sterile dropping pipette can be used to get an even covering of bacteria

Investigating the effect of antibiotics on bacterial growth

1. place paper discs soaked in different types of antibiotics on an agar plate that has an even covering of bacteria.

2. the antibiotic should diffuse into the agar jelly

3. place a control on the agar jelly

4. leave the plate for 48 hours at 25c

what are antibiotic resistant bacteria?

bacteria that will continue to grow around the paper discs while others die

What happens to non-resistant bacteria?

they will leave an inhibition zone around the paper disc (clear area)

What is the control used?

a paper disc not soaked in antibiotic but in sterile water- so you can be sure the difference between growth of bacteria is due to the antibiotic alone.

results

the more effective the antibiotic against the bacteria, the larger the inhibition zone

Similar method

testing the effects of antiseptics by replacing paper discs to soak in interested solutions

preparing an uncontaminated solution

1. sterilize petri dish and culture medium beforehand by heating at high temperature

2. if inoculating loop is used it should be sterilized first by passing through a hot flame

3. Work near a bunsen burner with a yellow flame to create a conv current above bench and destroy microorganisms in the air

4. after transferring bacteria, the petri dish lid should be lightly taped on to stop airborne microorganisms getting in

5. petri dish should be stored upside down to stop condensation falling on the agar surface an disrupting results

Measuring inhibition zone

1. calculate the area of the zone:

2. measure the diameter using a ruler

3. pi r squared

4. units- cm2 or mm2

5. then compare the area of all the zones