How does an allele conferring antibiotic resistance first arise in a bacterial population?

It arises by a random spontaneous mutation in the bacterial DNA, which happens whether or not the antibiotic is present.

Explain how using an antibiotic increases the proportion of resistant bacteria.

The antibiotic is a selection pressure that kills or halts the susceptible cells while the resistant ones survive, and because those survivors reproduce and pass the allele on, resistance forms an ever larger share of the population.

What is an R-plasmid?

An R-plasmid is a small circular loop of DNA, separate from the bacterial chromosome, that carries one or more genes for resistance to antibiotics.

How is a resistance plasmid passed from one bacterium to another?

It is passed by conjugation, in which a cytoplasmic bridge forms through a pilus between two cells and a copy of the plasmid is transferred along it.

Why is the transfer of resistance plasmids more dangerous than mutation alone?

A plasmid can move between bacteria of different species, and it often carries resistance to several antibiotics at once, so a harmless gut organism can hand multiple resistance to a pathogen in a single transfer.

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Immunology and Disease: Antibiotics

The spread of antibiotic resistance

3 things to know
Component 3

Overview

Recall questions on mutation as the source of resistance, selection under treatment, plasmids and horizontal transfer, why finishing a course matters, and both sides of the argument about wide prescribing.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Give three measures a hospital can take to slow the spread of resistant bacteria.

Key term

State the case for continuing to use antibiotics widely in medicine despite the rise of resistance.

Key term

Why does resistance spread far faster through bacteria than an adaptation does through an animal population?

Questions from this subtopic

Each one with the model answer underneath.

1
How does an allele conferring antibiotic resistance first arise in a bacterial population?
Model answer
It arises by a random spontaneous mutation in the bacterial DNA, which happens whether or not the antibiotic is present.
2
Explain how using an antibiotic increases the proportion of resistant bacteria.
Model answer
The antibiotic is a selection pressure that kills or halts the susceptible cells while the resistant ones survive, and because those survivors reproduce and pass the allele on, resistance forms an ever larger share of the population.
3
Why does resistance spread far faster through bacteria than an adaptation does through an animal population?
Model answer
Bacteria have generation times of minutes and reach enormous numbers, so mutations are common and selection acts over thousands of generations in days, and they can also pass genes sideways between living cells.
4
What is an R-plasmid?
Model answer
An R-plasmid is a small circular loop of DNA, separate from the bacterial chromosome, that carries one or more genes for resistance to antibiotics.
5
How is a resistance plasmid passed from one bacterium to another?
Model answer
It is passed by conjugation, in which a cytoplasmic bridge forms through a pilus between two cells and a copy of the plasmid is transferred along it.
6
Why is the transfer of resistance plasmids more dangerous than mutation alone?
Model answer
A plasmid can move between bacteria of different species, and it often carries resistance to several antibiotics at once, so a harmless gut organism can hand multiple resistance to a pathogen in a single transfer.

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