What is meant by a broad spectrum antibiotic?

A broad spectrum antibiotic is effective against a wide range of bacteria, including both Gram positive and Gram negative species.

What is meant by a narrow spectrum antibiotic?

A narrow spectrum antibiotic acts on only a limited group of bacteria, often only those of one wall type.

When is a broad spectrum antibiotic the right choice for a patient?

It is the right choice when the identity of the pathogen is not yet known and the patient is too ill to wait for culture results, or when several species are infecting the same site.

Give two advantages of using a narrow spectrum antibiotic once the pathogen has been identified.

It leaves most of the patient's harmless resident bacteria intact, and it applies the selection pressure for resistance to far fewer species.

Why does a broad spectrum antibiotic disturb the gut more than a narrow spectrum one?

It kills a large proportion of the normal gut flora as well as the pathogen, and the loss of that competition allows resistant bacteria and yeasts to multiply unchecked.

Name a broad spectrum antibiotic and state the range of bacteria it acts on.

Tetracycline is broad spectrum and acts on both Gram positive and Gram negative bacteria because it is small enough to cross the outer membrane.

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Immunology and Disease: Antibiotics

Broad and narrow spectrum antibiotics

3 things to know
Component 3

Overview

Broad spectrum antibiotic and narrow spectrum antibiotic.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Explain why the spectrum of an antibiotic depends on the structure of the bacterial cell wall.

Key term

Why does a broad spectrum antibiotic select for resistance in bacteria that are not causing the illness?

Key term

Suggest why an antibiotic acting on the bacterial ribosome is usually broader in spectrum than one acting on the wall.

Questions from this subtopic

Each one with the model answer underneath.

1
What is meant by a broad spectrum antibiotic?
Model answer
A broad spectrum antibiotic is effective against a wide range of bacteria, including both Gram positive and Gram negative species.
2
What is meant by a narrow spectrum antibiotic?
Model answer
A narrow spectrum antibiotic acts on only a limited group of bacteria, often only those of one wall type.
3
When is a broad spectrum antibiotic the right choice for a patient?
Model answer
It is the right choice when the identity of the pathogen is not yet known and the patient is too ill to wait for culture results, or when several species are infecting the same site.
4
Give two advantages of using a narrow spectrum antibiotic once the pathogen has been identified.
Model answer
It leaves most of the patient's harmless resident bacteria intact, and it applies the selection pressure for resistance to far fewer species.
5
Why does a broad spectrum antibiotic disturb the gut more than a narrow spectrum one?
Model answer
It kills a large proportion of the normal gut flora as well as the pathogen, and the loss of that competition allows resistant bacteria and yeasts to multiply unchecked.
6
Name a broad spectrum antibiotic and state the range of bacteria it acts on.
Model answer
Tetracycline is broad spectrum and acts on both Gram positive and Gram negative bacteria because it is small enough to cross the outer membrane.

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