What are antibiotics?
- 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.
1 of 5
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.
2 of 5
- 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.
3 of 5
- 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.
4 of 5
- 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.
5 of 5