Question: What are the main family of antibiotics by actions ? (beta-lactam , etc ... )

Robert Hampson answered on 18 Nov 2014:

There are (broadly speaking) four main mechanisms which I know about. They all stop (inhibit) a vital part of bacterial life.

The first inhibits the effective synthesis of the cell wall (these will only work well on bacteria without a second membrane outside their cell wall).

The second prevents the cell membrane functioning correctly (either by stopping it being made or by poking holes in it).

The third prevents proper synthesis of DNA and RNA. This can either be through preventing the cell making the individual building blocks of the RNA/DNA molecules or by preventing it from correctly reproducing DNA/RNA.

The fourth mechanism prevents the synthesis of proteins by the cell. These can be divided into two groups; one works on the large bit of the ribosome, the other group works on the small bit.

I have tried to summarise a bit below, but there is way too much to learn for me to try and explain all of antibiotics to you in one single answer. There are whole university modules which can last a whole year dedicated to antibiotics on their own.

Mechanism: Cell wall synthesis inhibitors
Classes which kill bacteria by this mechanism:
Beta lactam antibiotics (there are hundreds of these with separate subclasses of their own),
Glycopeptide antibiotics (including vancomycin, teicoplanin, etc.),
Some polypeptide antibiotics (bacitracin for example)

Mechanism: Cell membrane inhibitors (there aren’t many of these because human cells have cell membranes which are similar to bacteria)
Classes which kill bacteria by this mechanism:
Some polypeptide antibiotics (polymixin for example)

Mechanism: Nucleic Acid synthesis inhibitors
Classes which kill bacteria by this mechanism:
Folate synthesis inhibitors (they inhibit the way the bacteria makes the building blocks of DNA, they include two different types of chemical: sulfonamide antibiotics and trimethoprim – these two are generally given together),
DNA gyrase inhibitors (these prevent the bacteria copying its DNA effectively, they include the quinolones)
RNA polymerase inhibitors (they stop the bacteria making RNA like Rifampin)

Mechanism: Protein synthesis inhibitors acting on 50S subunit of ribosome (the big bit)
Classes which kill bacteria by this mechanism:
Macrolides,
Streptogramins,
Oxazolidenones,
Chloramphenicol (only one in this class!),
Lincosamides

Mechanism: Protein synthesis inhibitors acting on 30S subunit of ribosome (the small bit)
Classes which kill bacteria by this mechanism:
Tetracyclins,
Aminoglycosides

Hope that helps! But like I say, it is quite complicated!