How antibiotics work

Antibiotics are drugs that kill or inhibit the growth of bacteria. They target the bacterial enzymes and ribosomes used in metabolic reactions, meaning they do not damage human cells (as they contain different enzymes and ribosomes). 

Examples of how antibiotics affect bacteria include: 

• Preventing the synthesis of bacterial cell walls.
• Disrupting protein activity in the cell membrane.
• Disrupting enzyme action.
• Preventing DNA synthesis.
• Preventing protein synthesis.

Antibiotics do not work against viruses because viruses lack cell structures, instead relying on host cells to carry out metabolic reactions. This means that antibiotics cannot target and disrupt these reactions. Furthermore, antibiotics are unable to reach viruses as they invade the organism's own cells. 

Penicillin 

One of the first antibiotics to be discovered was penicillin. It was discovered by Alexander Fleming when he found the mould, Penicllium chrysogenum, growing on his bacterial cultures. 

Penicillin inhibits the growth of bacteria by preventing the formation of bacterial cell walls. It inhibits the enzymes responsible for building cross-links between peptidoglycan polymers.

Actively growing bacteria secrete enzymes known as autolysins which make tiny holes in the cell wall, allowing the wall to stretch so that new peptidoglycan chains can link together. Penicillin prevents the linking of peptidoglycan chains, but the autolysins continue to make holes. This weakens the cell wall, causing the bacterial cells to burst when water enters by osmosis. 

Antibiotic resistance

Following the discovery of penicillin in the mid-20th century, antibiotics have been used to successfully treat numerous bacterial infections. This drastically reduced the number of deaths due to communicable diseases.

However, their increased use has led to the development of antibiotic resistant bacteria. This means that antibiotics that were once effective against these bacteria no longer work, making it much more difficult to treat bacterial infections.

Antibiotic resistance develops via natural selection:

1. Genetic mutations occur, making some bacteria resistant to an antibiotic.
2. When an infection is treated with antibiotics, resistant bacteria are able to survive.
3. Resistant bacteria reproduce, passing on the allele for antibiotic resistance to their offspring.

Genes for antibiotic resistance often occur on plasmids, meaning they can also be transferred from one bacterium to another in the process of conjugation. 

The impact of antibiotic resistance

The development of antibiotic resistant bacteria is a problem because it means that bacterial infections are becoming more difficult to treat. 

Some bacteria have developed resistance for several different antibiotics, such as methicillin-resistant Staphylococcus aureus (MRSA). This bacteria has become a problem in hospitals around the world as there are very few antibiotics that are now effective against this bacteria. 

The following measures can help reduce the development of antibiotic resistance: 

1. Choosing appropriate antibiotics for treatment - Antibiotics can be tested against bacterium strains to make sure they are effective in treating the disease.
2. Using antibiotics only when needed - Antibiotics should only be prescribed for bacterial infections, not for viral infections. 
3. Avoiding the use of wide-spectrum antibiotics - The use of narrow-spectrum antibiotics (antibiotics specific for the infection) is less likely to lead to antibiotic resistance.
4. Ensuring that patients complete courses of antibiotic treatment - This ensures all bacteria are killed and so does not give them the chance to develop resistance.
5. Avoiding the use of antibiotics in farming - This reduces the chance of bacteria becoming resistant to antibiotics.