Antiseptics and antibiotics

Bacteria can become resistant to antibiotic due to bacteria mutating. If you have an infection some of the bacteria is resistant to antibiotic so only the non-resistant strains of bacteria will be killed. The individual resistant bacteria will reproduce and the population of the resistant strain will increase; natural selection. The resistant strain can cause a serious infection that cannot be treated by antibiotics. E.g MRSA causes serious wound infections and is resistant to the powerful antibiotic Methicillin.

Practical to investigate

Pour hot sterilised agar jelly into a sterile petri dish, when the jelly is set transfer bacteria to the culture medium. Then take three paper discs; soak one in antibiotic, another in different antibiotic and the third in sterile water. Place the discs in the jelly and tape the lid. Leave the dish for 24 hours at 25 degrees. Look at the results, anywhere the bacteria can’t grow is called an “inhibition zone” the bigger the inhibition zones around the disc, the more effective the antibiotics. The control variables for this experiment include; Temperature, size of the discs, concentration of the antibiotics.

	Created by daniifarrell over 12 years ago

GCSE Biology Core Note on Inter-relationships, created by daniifarrell on 02/01/2014.