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Antibiotic resistance

The evolution of strains of bacteria that are not affected by a particular antibiotic as a result of natural selection.

selection pressure

Stresses on a specific environment that affect an organism’s ability to survive eg resource availability or temperature.

Natural selection

The process in nature where the fittest individuals survive, reproduce and pass their characteristics on to their offspring.

genetic drift

Random mutations occurring and accumulating in a population over time.

conjugation

The transfer of genetic material between bacterial cells by direct contact.

Nucleotide

Monomer unit of the nucleic acids DNA and RNA. Each nucleotide is made up of three parts: a pentose sugar, a phosphate group and a nitrogenous base.

Mutation

A change in the arrangement or amount of genetic material in a cell.

Evolution

A theory, supported by much evidence, which suggests that the animal and plant species inhabiting the earth today are descended from simpler forms by a gradual process of change.

Microbes

Microorganisms such as bacteria, yeasts and fungi

Plasmid

A small circle of extra DNA found in bacteria

Development of antimicrobial resistance

Microorganisms are gaining resistance to antimicrobials - this is called antimicrobial resistance. This is often also called antibiotic resistance.

How does antimicrobial resistance develop?

Microorganisms mutate in a random process called genetic drift. These mutations create microorganisms with a range of phenotypes. Some of these microorganisms will be resistant to antimicrobials.

Natural selection occurs when antimicrobials are used; antimicrobial medicines act as a selection pressure. Only resistant microbes can survive and reproduce. These microorganisms will pass on their resistance to offspring, passing on their selective advantage.

The diagram below summarises the development of antimicrobial or antibiotic resistance.

Development of resistance

How does antimicrobial resistance spread?

Once a microbe has developed resistance, it can pass it on to its offspring. Alternatively, bacteria can share plasmids that code for antibiotic resistance between each other via conjugation.

Genetic drift in Staphylococcus aureus

Staphylococcus aureus bacteria shown under scanning electron micrograph

S. aureus divides every 30 minutes. If you start with one S. aureus bacterium, it would take only 5 hours for that single cell to grow into a colony of 1,024 cells. After 5 more hours, the population size will be 1,048,576 cells.

S. aureus has approximately 2.8 million nucleotide base pairs in its genome. If the mutation rate were 10-10 mutations per nucleotide base there would be 300 mutations in that population of cells within 10 hours!

Exam style question

Discussion point

Antimicrobial resistance development is an example of evolution via natural selection.

What are some other examples of natural selection?

Exam style questions

Decide whether each of the following statements about antimicrobial resistance are true or false:

1. Humans are developing resistance to antimicrobial medicines.
TRUE
FALSE
TRUE
(The correct answer is:
'FALSE')
FALSE
null
(The correct answer is:
'FALSE')
null
(The correct answer is:
'FALSE')
null
(The correct answer is:
'FALSE')
2. Antimicrobial resistance only develops when antimicrobials are used.
TRUE
FALSE
TRUE
(The correct answer is:
'FALSE')
FALSE
null
(The correct answer is:
'FALSE')
null
(The correct answer is:
'FALSE')
null
(The correct answer is:
'FALSE')
3. Bacteria can share DNA via conjugation.
TRUE
FALSE
TRUE
FALSE
(The correct answer is:
'TRUE')
null
(The correct answer is:
'TRUE')
null
(The correct answer is:
'TRUE')
null
(The correct answer is:
'TRUE')
4. Antibiotics are useful for treating viral infections.
TRUE
FALSE
TRUE
(The correct answer is:
'FALSE')
FALSE
null
(The correct answer is:
'FALSE')
null
(The correct answer is:
'FALSE')
null
(The correct answer is:
'FALSE')

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One-page summary