Antibiotics (Cambridge (CIE) O Level Biology): Revision Note

Using Antibiotics

• Antibiotics are a kind of drug

  • A drug is any substance taken into the body that modifies or affects chemical reactions in the body

• Antibiotics are chemical substances made by certain fungi or bacteria that affect the working of bacterial cells, either by disrupting their structure or function or by preventing them from reproducing.

• Antibiotics are effective against bacteria but not against viruses

• Antibiotics target processes and structures that are specific to bacterial (prokaryotic) cells; as such they do not generally harm animal cells

How Antibiotics Work Diagram

How antibiotics work

Effectiveness of Antibiotics

• Some bacteria that cause disease have become resistant to antibiotics and this reduces the effectiveness of prescribed antibiotics when someone has a bacterial infection, as it might be caused by a type of bacteria that is resistant to that particular antibiotic

Why don't Antibiotics Affect Viruses?

• Viruses cannot be treated with antibiotics

• This is because antibiotics work by disrupting cell functions such as respiration, or breaking down the structure of the cell in some way

• However, viruses do not carry out any cell functions and do not have cell walls, cell membranes or any cell organelles as viruses infect and utilise the machinery of animal cells to reproduce, which are not affected by antibiotics.

• Therefore the action of antibiotics do not affect them

Antibiotic Resistance

• Since the first antibiotic was discovered in 1928, many more have been discovered and developed and antibiotics were and are widely overused

• Commonly prescribed antibiotics are becoming less effective due to a number of reasons:

  • overuse and being prescribed when not really necessary

  • patients failing to complete the fully prescribed course by a doctor

  • large-scale use of antibiotics in farming to prevent disease when livestock are kept in close quarters, even when animals are not actually sick

• This has led to the effectiveness of antibiotics being reduced, and the incidence of antibiotic resistance increasing

• These bacteria are commonly known as superbugs and the most common is MRSA

• Ways individuals can help prevent the incidence of antibiotic resistance from increasing include:

  • only taking antibiotics when absolutely essential

  • when prescribed a course of antibiotics, ensure that the entire course is completed even if you feel better after a few days

Antibiotic resistance