Interactive resources for schools

Select an age range to seek interactive content for...

classes of antibiotics

A group of antibiotics with the same mode of action.

Antibiotic

Medicine that acts against bacterial infections. Penicillin is an example of an antibiotic.

Protein

A polymer made up of amino acids joined by peptide bonds. The amino acids present and the order in which they occur vary from one protein to another.

Cell

The basic unit from which all living organisms are built up, consisting of a cell membrane surrounding cytoplasm and a nucleus.

DNA

Deoxyribonucleic acid. This is the molecule which contains the genetic code. It coils up tightly inside chromosomes. DNA is a double helix made from two strands which are joined together by pairs of bases.

What are antimicrobials?

Antimicrobials are a group of medicines used to treat infections. This group includes antibiotics (which treat bacterial infections) and antifungals (which treat fungal infections). Neither antibiotics nor antifungals are capable of treating viral infections.

Many antimicrobials are produced in nature by soil bacteria and fungi. This enables the microorganism to kill off its competition and consequently have an advantage in its environment when competing for limited resources.

Discovery of antimicrobials

Before antimicrobials were discovered, many people died from infections that today are easily treated. The discovery of antimicrobials transformed global health and revolutionised medicine.

Alexander Fleming

Alexander Fleming discovered the first antibiotic, penicillin, in 1928. Fleming noticed that bacterial growth had been inhibited on a petri dish accidentally contaminated with the mould Penicillium notatum. He realised that the mould must be producing a compound inhibiting bacterial growth. This compound was penicillin. Two researchers at Oxford University, Howard Florey and Ernst Chain, investigated Fleming’s work further and showed that penicillin could be used to treat infections in patients. In 1945, Fleming, Florey and Chain shared the Nobel Prize in Physiology or Medicine for “the discovery of penicillin and its curative effect in various infectious diseases”.

Rachel Fuller Brown and Elizabeth Lee Hazen

The first antifungal, nystatin, was discovered in 1949 by Rachel Fuller Brown and Elizabeth Lee Hazen. Hazen cultured bacteria from soil samples collected all over the US. She then tested to see if any of the compounds the bacteria produced were effective at killing fungi. When she saw something promising, she sent it in the post to Brown, who isolated and purified the compounds. Brown then posted the compounds back to Hazen who tested them on the fungi again and then if effective, tested them on animals. This went on until they found an active non-toxic compound. The compound they discovered was nystatin, which remains an effective treatment for skin, mouth, vaginal and intestinal tract fungal infections.

There are now hundreds of antibiotics on the market, the majority of which come from a limited number of classes of antibiotics. There are far fewer antifungals on the market, only approximately 20 in total.

How do antimicrobials work?

Antimicrobials take advantage of the structural differences between microorganisms and human cells.

Antimicrobial modes of action can be classified as either:

  1. –static (they inhibit the growth of microorganisms)
  2. –cidal (they kill the microorganism)

Antimicrobials target specific parts of the microorganism. Due to structural variation between microorganisms, antimicrobials are only active against individual species or groups of species.

Based on specificity antimicrobials can be classified as either:

  1. broad spectrum (target a wider range of microorganisms)
  2. narrow spectrum (target either a single species or a few species)

Specific antimicrobial mechanisms are shown in the diagrams below.

Antibiotics: mechanisms of action

Show animation full screen in new window
Antifungals: mechanisms of action

Show animation full screen in new window

Exam style questions

Select the correct option:

1. Who discovered penicillin in 1928?
Joseph Lister
Alexander Fleming
Louis Pasteur
Joseph Lister
(The correct answer is:
'Alexander Fleming')
Alexander Fleming
Louis Pasteur
(The correct answer is:
'Alexander Fleming')
null
(The correct answer is:
'Alexander Fleming')
null
(The correct answer is:
'Alexander Fleming')
2. In what year did Rachel Fuller Brown and Elizabeth Lee Hazen discover nystatin?
1949
1929
1940
1949
1929
(The correct answer is:
'1949')
1940
(The correct answer is:
'1949')
null
(The correct answer is:
'1949')
null
(The correct answer is:
'1949')
3. Antimicrobials that kill microorganisms are classified as:
–static
–cidal
–cryptic
–static
(The correct answer is:
'–cidal')
–cidal
–cryptic
(The correct answer is:
'–cidal')
null
(The correct answer is:
'–cidal')
null
(The correct answer is:
'–cidal')
4. Which process do antibiotics but not antifungals target?
protein synthesis
cell wall synthesis
DNA replication
protein synthesis
cell wall synthesis
(The correct answer is:
'protein synthesis')
DNA replication
(The correct answer is:
'protein synthesis')
null
(The correct answer is:
'protein synthesis')
null
(The correct answer is:
'protein synthesis')

Possible further reading

Antibiotics, NHS
Antifungals, NHS
Antimicrobial agents in the treatment of infectious disease, Todar’s Online Textbook of Bacteriology

Click to download the key word summary shown below.

Key word summary