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. 

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.