Macrolide

Macrolides are antibiotics characterized by a large macrocyclic lactone ring. They bind the bacterial 50S ribosomal subunit and inhibit protein synthesis.

Bacterial ribosome: The RNA–protein complex that translates messenger RNA into proteins in bacteria. Macrolides act on its 50S subunit to disrupt bacterial protein synthesis.
Azithromycin: A semisynthetic azalide antibiotic related to macrolides, used for selected bacterial infections. Its long tissue persistence and dosing schedule distinguish it from older macrolides.
Macrolactone: A cyclic ester containing a large ring, formed by intramolecular esterification. The macrocyclic lactone ring is the defining structural feature of macrolide antibiotics.
Lincosamide: An antibiotic class, including clindamycin, that inhibits bacterial protein synthesis at the 50S ribosomal subunit. Lincosamides overlap with macrolides in binding region and resistance patterns but have different structures.
Erm methyltransferase: A bacterial enzyme that methylates 23S ribosomal RNA and can confer resistance to several antibiotic classes. This modification reduces macrolide binding and can produce cross-resistance to lincosamides and streptogramins.
50S ribosomal subunit: The large subunit of the bacterial ribosome, containing 23S and 5S ribosomal RNA and proteins. Macrolides bind near the peptide exit tunnel within this subunit.
Clarithromycin: A semisynthetic macrolide antibiotic used for selected respiratory and other bacterial infections. It is one of the class’s commonly used agents and a component of some Helicobacter pylori regimens.
Desosamine: A deoxy amino sugar found in several macrolide antibiotics. This sugar contributes to macrolides’ binding to the bacterial ribosome.
Tetracycline: An antibiotic class that inhibits bacterial protein synthesis by binding the 30S ribosomal subunit. Tetracyclines target the small subunit rather than macrolides’ 50S site.
Efflux pump: A membrane protein complex that transports substances out of a cell. Bacterial efflux pumps can export macrolides and lower their intracellular concentration.

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