Substances produced by living organisms that can inhibit the growth of or destroy microorganisms.
Used to treat bacterial infections and dieseases. They have not effect on viruses.
Can be made synthetically or semi-synthetically.
First discovered by accident by Alexander Fleming in 1928. He discovered penicillin which was the first antibiotic to be used.
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How do antibiotics work?
Prevent bacteria from making normal cell walls.
When bacteria are actively dividing the antibiotic prevents cross links from forming between the cellulose chains that give the cell wall its strength.
The cell wall stops the bacterial cell from bursting when water enters it.
As the peptide cross links cannot form when water enters the cell the cell wall cannot resist the pressure and the cell bursts, killing it. This is known as osmotic lysis.
Only works if bacteria are actively dividing as it prevents the cross links from forming.
Do not work on viruses as they have a different coating to bacteria.
Penicillin works in this way.
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Antibiotic resistance
Resistance is due to mutations is the DNA of the bacteria, producing a protein that provides resistance, either by destroying the antibiotic or some other method.
It is not the presence of the antibiotic that causes the bacteria to mutate. They happen by chance.
The mutant gene is then passed on to the next generation of bacteria by vertical gene transmission.
The mutant gene is passed on to other species of bacteria by horizontal gene transmission.
Bacteria that posess the mutant gene will not be killed by the antibiotic and can survive to multiply.
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Tuberculosis
Antibiotics must be taken for a long period of time.
Initially they kill the least resistant strains of bacteria, which makes the patient feel better so sometimes they stop taking the antibiotics.
The most resistant strains are then left and can divide without the antibiotic being there to kill them. These are then spread to other people.
This leads to the development of strains that are resistant to the antibiotic.
Other strains can recieve the mutant gene by horizontal gene transmission.
So strains that are resistant to multiple antibiotics are produced.
Then a cocktail of antibiotics have to be taken to ensure all the bacteria are killed as so many are now resistant.
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MRSA
MRSA stands for methicillin resistant Staphylococcus aureus.
MRSA is especially prevelent in hospitals and is dangerous because the people tend to be old and are sicker and weaker than normal so they are more vulnerable to infection.
Doctors and nurses come into contact with many patients which spreads infection.
Many antibiotics are used in hospitals so mutant strains have an advantage over non-mutant strains. As many different antibiotics are used strains easily develop multiple resistance.
MRSA is difficult to treat because it has developed resistance to almost every known antibiotic.
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