Pupil Activities:
these activities can be done on-line or the worksheet can be downloaded and used in conjunction with the experiments in the lab.

All microbe experiments must be carried out using the appropriate safety precautions see any suitable microbiology book.

1. Fleming's Discovery:

Remember that you need to check with your teacher about how to carry out microbiology safely, Alexander Fleming would not have passed to-day's safety procedures!

To reproduce Alexander Fleming's experiment you need a nutrient agar plate growing a suitable culture, not Staphlocococcus but Micrococcus luteus would be OK.

Add a small square of Penicillium notatum,using sterile techniques, seal the plate, incubate at room temperature and observe the growth of the bacterial culture.

Your results could be recorded by drawing the incubated plate, you can also measure the diameter of the zone of inhibition (the clear area around the fungus)

When you have finished make sure the plate is disposed of safely.

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2. How does penicillin  work

The picture on the left shows Bacillus cereus growing

On the right we have the same bacteria growing with low concentrations of penicillin; because the antibiotic affects the cross linking of the cell walls,  the cells are larger ( less cell divisions)

thanks to Jim Deacon of the University of Edinburgh, more information can be found at his website, see the reference section

Penicillin works by blocking cell wall synthesis, specifically affects the production of peptidoglycans so that the cell wall lacks strength. Eventually the cell collapses . Only Gram positive bacteria are affected because they have a significant amount of peptidoglycan in their cell wall

How do other antibiotics work?

1. Using a suitable textbook or website find a diagram of a bacterial cell, do a simple line drawing showing cell wall, ribosomes, membrane, cytoplasm, nuclear material.Add to your diagram the  sites where antibiotics work

2. Find out what effect each of these antibiotics has on bacteria, complete the table

3.Build a glossary /notes on antibiotics

these are words you should know the meaning of:

Which antibiotic is best?

When a person attends the doctor with an unknown bacterial infection it is
necessary to quickly find out which antibiotic will work. 

For this process, a multidisc is used. A multidisc is made of sterile filter paper with a different type of antibiotic on each arm. 

A sample of bacteria is spread across an agar plate and the multidisc put on top.

 Clear areas around the arm of the multidisc indicate that the bacteria is sensitive to that antibiotic.

* Your teacher can show you an agar plate containing a multidisc.or use the information below

key: clockwise from top; Novobiocin; penicillin G, dark pink; streptomycin, white; tetracycline; chloramphencol, light yellow; erythromycin; fuscidic acid,green; methicillin. thanks to J.Deacon, University of Edinburgh

1. Measure the zones of inhibition (clear areas around the different antibiotics).  Which is the best way to do this ? Record this information in a table.

Problems with antibiotics

1. Allergies
A significant number of people are allergic to penicillin.
What happens if they are given penicillin?

Are you ?

if you want to find out more, go to http://www.mayohealth.org/mayo/9812/htm/penicil.htm

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2. Resistance

Bacteria can easily develop resistance to antibiotics. Penicillin resistance is due to the bacteria producing an enzyme ( B-lactamase) which breaks down penicillin.

thanks to J.Deacon University of Edinburgh

How does this happen?
Treating the disease with penicillin selects for those organisms which contain the genes that produce the enzyme.

See how it works
Click here the link to see a PowerPoint presentation

The more widespread the use of a drug is the more likely resistance is to develop. For example in1985 in Austria 45% of sepsis infections [Staphylococcal pyogenes aureus ] infections were resistant to streptomycin. How do we try to limit the build up of resistance
Doctors have to be carefully which antibiotic they use?

If you are given an antibiotic, finish the course
Don't always expect an antibiotic, coughs and colds are usually caused by viruses, antibiotics have no effect

If resistance has appeared then combinations of antibiotics are given for example in treating TB or leprosy

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