The Evolution of Antibiotic-Resistance in Bacteria

Antibiotic-Resistant Bacteria The bacteria growing around this disk soaked in antibiotic are not affected by it – they are resistant to it

Antibiotic-Resistant Bacteria In 2012, 292 people died in UK hospitals as a result of infection with Methicillin Resistant Staphylococcus aureus (MRSA). As its name suggests, MRSA cannot be treated with the antibiotic Methicillin. Infection can spread quickly in hospitals – why do you think this is?

Lesion caused by Staphylococcus aureus

Antibiotic-Resistant Bacteria Using your knowledge of evolution by means of natural selection, can you explain how resistance can develop and spread through bacterial populations? selective advantage random mutation selection pressure antibiotic survive reproduce

The Four Steps of Natural Selection Copy & highlight key words as you go There is genetic variation within a species. This variation can be due to mutations (which make new genes) or sexual reproduction (which mixes up genes). Most offspring die young, before they can reproduce. They die from predation, disease or competition for resources because they are genetically “weak” (i.e. not so well adapted to their environment). The best individuals, who are genetically “fit” (i.e. well adapted to their environment) live long and reproduce often, passing their good genes on to their offspring. This is the selection stage. This selection is repeated each generation. After very many generations the characteristics of a whole species can change.

Antibiotic-Resistant Bacteria Bacteria are everywhere They can develop random mutations in their DNA which can make them resistant to a particular antibiotic. If this antibiotic is present in their environment (e.g. in a hospital), any bacteria with resistance will survive and reproduce asexually, passing the resistance gene onto all their offspring. Non-resistant bacteria will be killed. Bacteria reproduce rapidly (every 20 minutes) – there could be 72 generations by the end of one day! If the antibiotic remains in the environment, the resistant bacteria will replace all non-resistant types

Superbugs – Multi-Antibiotic-Resistant Bacteria Bacteria can pass genetic material between each other (even between species). In this way a harmless bacteria that has randomly developed resistance to an antibiotic could pass on this resistance to a more harmful type. If the antibiotic is present, these new strains will flourish.

Deaths due to MRSA have fallen by 75% between 2008 and 2012 Deaths due to MRSA have fallen by 75% between 2008 and 2012. How do you think this decrease was achieved? Restricted use of antibiotics Better education on ‘finishing the course’ Cleaner hospitals Measures to reduce infection & spread of bacteria in hospitals Careful selection of appropriate antibiotics and dosage Remember, there is NOTHING we can do to prevent the mutations that cause resistance, but we can all act to reduce the likelihood of resistance spreading. Bacteria have been found that are resistant to ALL known antibiotics.

Superbugs – Multi-Antibiotic-Resistant Bacteria Bacteria can become resistant to more than one antibiotic. The resistance is always caused by a random mutation, but if the bacteria are exposed to more than one type of antibiotic, although they will more than likely be killed, a second mutation could occur. In this way, a bacterium could become resistant to 2 or more antibiotics at once.

Counter demonstration