Evidence for evolution - resistant bacteria

Antibiotic resistance

Bacteria can evolve quickly because they reproduce at a fast rate. Mutations of bacteria can produce new strains. Some bacteria might become resistant to certain antibiotics, such as penicillin, and cannot be destroyed by the antibiotic. The evolution of the bacteria is an example of natural selection.

Development of resistance

The main steps in the development of resistance are:

  1. random mutations occur in the genes of individual bacterial cells
  2. some mutations protect the bacterial cell from the effects of the antibiotic
  3. bacteria without the mutation die or cannot reproduce when the antibiotic is present
  4. resistant bacteria can reproduce with less competition from normal bacterial strains
Bacteria can evolve quickly because they reproduce at a fast rate.


The number of resistant strains has increased, partly due to the misuse of antibiotics. This has resulted in more infections that are difficult to control.

MRSA is methicillin-resistant Staphylococcus aureus, and it is very dangerous because it is resistant to most antibiotics.

In order to reduce the rate of development of antibiotic resistant strains:

  • doctors should not prescribe antibiotics inappropriately, such as for the treatment of non-serious infections
  • patients should always complete the full course of antibiotics to ensure all bacteria are killed and none survive to mutate and form resistant strains
  • the agricultural use of antibiotics should be restricted
An agar plate containing penicillin

Penicillin was the first antibiotic to be produced on a mass scale in the 1940s. It is derived from Penicillium fungus, shown here growing on an agar plate.

Some antibiotics are kept in reserve as a last resort – when others fail. But some bacteria are now becoming resistant to these.

The development of new antibiotics has slowed in recent years. Drugs companies have little financial incentive to develop antibiotics that would only be used very occasionally if none of the other types worked.

Antibiotic development has now increased again, however, as governments realise that this will be required to avert a global catastrophe. Drugs companies are also adopting new strategies to kill bacteria - one approach might make bacteria suicidal. Researchers are also investigating the genomes of pathogens and researching genomic approaches to fighting disease.