Antibiotics

Antibiotics are chemicals that many fungi produce. Antibiotics kill a wide range of bacteria without harming us. In 1928 Alexander Fleming noticed that bacteria had not grown in an area surrounding some mould on an agar plate. He realised that some antibacterial agent had stopped the bacteria growing there. He later discovered that this antibacterial agent was penicillin and was released by the mould Penicillium notatum. This antibiotic was first extracted in 1942. Penicillin naturally works by preventing other fungi and bacteria from growing close to Penicillium notatum mould. This reduces competition for nutrition, space, and water. Penicillin is still widely used today as a drug to kill pathogenic bacteria. There are now many types of antibiotics used in medicine. Different antibiotics work in different ways to kill bacteria. Antibiotics cannot kill viruses. They will have no effect on the viruses that cause common colds and the flu.

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Bacterial Resistance to Antibiotics

Since the discovery of penicillin, other natural antibiotics have been discovered and many have been synthesised (made) by scientists in laboratories. Over the past 20-30 years their use has increased dramatically. Often we expect to be given an antibiotic by our doctor, even for minor illnesses that don't really need them. The over prescribing and over use of antibiotics can be dangerous, as this can lead to bacteria becoming resistant to antibiotics.

In all populations of living things there is variation (natural variation in the species), and mutations can happen all the time. In a population of bacteria there could be a chance mutation that leads to a bacterium being resistant to a particular antibiotic. In this situation when antibiotics are often used, the the new resistant bacterium will have an advantage over non-resistant bacteria of the same type (type with a selective advantage). The resistant type of bacterium will survive and multiply in great numbers (type selected for), and the non-resistant bacteria will not survive (type selected against). Since bacteria reproduce very rapidly by binary fission, very soon you will have a population with many resistant bacteria and fewer non-resistant bacteria. After many generations the population of bacteria could become almost entirely made up of resistant bacteria (result of natural selection over many generations). Doctors would then have to find another antibiotic to treat the infection, one that there are not strains of bacteria that are resistant to.

Doctors are becoming more reluctant to prescribe antibiotics. By using fewer antibiotics, bacteria with resistance will have less of a selective advantage and will not become so widespread.

The diagrams below show how bacteria can become resistant to antibiotics.

How Resistant Bacteria Come About