Drug Action Drug Receptors Drugs of C.N.S  Elmhurst College Enzyme Inhibition Sulfa Drugs Cancer Drugs I  Chemistry Department Penicillin Other Antibiotics Cancer Drugs II  Virtual ChemBook

	Other Antibiotics Macrolides - Erythromycin, Azithromycin: Macrolides are products of actinomycetes (soil bacteria) or semi-synthetic derivatives of them. Erythromycin is an orally effective antibiotic discovered in 1952 in the metabolic products of a strain of Streptocyces erythreus, originally obtained from a soil sample. Mechanism of Action Erythromycin and other macrolide antibiotics inhibit protein synthesis by binding to the 23S rRNA molecule (in the 50S subunit) of the bacterial ribosome blocking the exit of the growing peptide chain. of sensitive microorganisms. (Humans do not have 50 S ribosomal subunits, but have ribosomes composed of 40 S and 60 S subunits). Certain resistant microorganisms with mutational changes in components of this subunit of the ribosome fail to bind the drug. The association between erythromycin and the ribosome is reversible and takes place only when the 50 S subunit is free from tRNA molecules bearing nascent peptide chains. Gram-positive bacteria accumulate about 100 times more erythromycin than do gram-negative microorganisms. The non ionized from of the drug is considerably more permeable to cells, and this probably explains the increased antimicrobial activity that is observed in alkaline pH. Review RNA types Erythromycin - Chime in new window
Some clinically important antibiotics Antibiotic Producer organism Activity Site or mode of action Penicillin Penicillium chrysogenum Gram-positive bacteria Wall synthesis Cephalosporin Cephalosporium acremonium Broad spectrum Wall synthesis Griseofulvin Penicillium griseofulvum Dermatophytic fungi Microtubules Bacitracin Bacillus subtilis Gram-positive bacteria Wall synthesis Polymyxin B Bacillus polymyxa Gram-negative bacteria Cell membrane Amphotericin B Streptomyces nodosus Fungi Cell membrane Erythromycin Streptomyces erythreus Gram-positive bacteria Protein synthesis Neomycin Streptomyces fradiae Broad spectrum Protein synthesis Streptomycin Streptomyces griseus Gram-negative bacteria Protein synthesis Tetracycline Streptomyces rimosus Broad spectrum Protein synthesis Vancomycin Streptomyces orientalis Gram-positive bacteria Protein synthesis Gentamicin Micromonospora purpurea Broad spectrum Protein synthesis Rifamycin Streptomyces mediterranei Tuberculosis Protein synthesis	Tetracyclines: Tetracyclines have the broadest spectrum of antimicrobial activity. These may include: Aureomycin, Terramycin, and Panmycin. Four fused 6-membered rings, as shown in the figure below, form the basic structure from which the various tetracyclines are made. The various derivatives are different at one or more of four sites on the rigid, planar ring structure. The classical tetracyclines were derived from Streptomyces spp., but the newer derivatives are semisynthetic as is generally true for newer members of other drug groups. Mechanism of Action: Tetracyclines inhibit bacterial protein synthesis by blocking the attachment of the transfer RNA-amino acid to the ribosome. More precisely they are inhibitors of the codon-anticodon interaction. Tetracyclines can also inhibit protein synthesis in the host, but are less likely to reach the concentration required because eukaryotic cells do not have a tetracycline uptake mechanism.
Click for larger image	Streptomycin: Streptomycin is effective against gram-negative bacteria, although it is also used in the treatment of tuberculosis. Streptomycin binds to the 30S ribosome and changes its shape so that it and inhibits protein synthesis by causing a misreading of messenger RNA information. Chloramphenicol: Chloromycetin is also a broad spectrum antibiotic that possesses activity similar to the tetracylines. At present, it is the only antibiotic prepared synthetically. It is reserved for treatment of serious infections because it is potentially highly toxic to bone marrow cells. It inhibits protein synthesis by attaching to the ribosome and interferes with the formation of peptide bonds between amino acids. It behaves as an antimetabolite for the essential amino acid phenylalanine at ribosomal binding sites. Link to site explaining how bacteria become resistant to chloramphenicol - contains Chime molecules