Erythromycin antibiotic is synthesised by Streptomyces erythraeus. It is usually bacteriostatic and binds with the 23SrRNA of the 50S ribosomal subunit to inhibit peptide chain elongation during protein synthesis. Erythromycin is a relatively broad-spectrum antibiotic it is effective against Gram-positive bacteria mycoplasmas and a few Gram-negative bacteria.