Resistant bacteria: doctors should not prescribe antibiotics inappropriately, such as treating non-serious or viral infections

The idea

Antibiotics kill bacteria by disrupting cell wall formation, protein synthesis or DNA replication, but they have no effect on viruses because viruses lack these bacterial targets and reproduce inside host cells. Prescribing antibiotics for a viral infection such as influenza or the common cold therefore gives no benefit to the patient while exposing the patient's bacteria to the drug. Any bacterium with a random mutation that lets it survive is more likely to reproduce, so the resistant allele increases in the population. Doctors reduce this selection pressure by prescribing antibiotics only when a bacterial infection is likely and the illness is serious enough to need them, for example a confirmed bacterial chest infection, rather than a mild sore throat that is probably viral.

What earns the marks

• Antibiotics kill bacteria but do not kill viruses, because viruses do not have the bacterial structures that antibiotics target.
• Prescribing antibiotics for a viral infection gives no benefit to the patient and does not treat the cause of the illness.
• Unnecessary antibiotic use exposes bacteria in the patient and environment to the drug, selecting resistant bacteria that survive and reproduce.
• Doctors should prescribe antibiotics only when a bacterial infection is likely and treatment is needed, for example a serious bacterial infection rather than a mild self-limiting illness.
• Reducing inappropriate prescribing lowers the selection pressure that leads to resistant strains, helping antibiotics remain effective.

Common mistakes and how to put them right

• Thinking antibiotics can treat viral infections such as colds or influenza.

  Put it right: Antibiotics act only on bacteria, so viral infections need other management such as rest, fluids or antiviral drugs where appropriate.

• Believing that inappropriate prescribing harms only the individual patient.

  Put it right: It also selects resistant bacteria that can spread to other people, so it is a wider public-health problem.

• Assuming a doctor can always tell instantly whether an infection is bacterial or viral.

  Put it right: Diagnosis may use symptoms, tests or waiting to see how the illness develops, and antibiotics are prescribed only when a bacterial cause is likely.

Exam tips

• Link the answer to natural selection: state that random mutation can produce resistant bacteria, then antibiotics kill non-resistant bacteria while resistant ones survive and reproduce.
• Use the phrase selection pressure when explaining why unnecessary prescribing increases resistance.
• Give a named example of an inappropriate use, such as treating a viral cold with antibiotics, and a contrasting appropriate use, such as treating a serious bacterial infection.