Cephalosporins:

Originally isolated fromthe fungus Cephalosporium in 1948 and their β -lactam ring structure is very similar to that of penicillins and resembles them in inhibiting cell wall synthesis or the transpeptidation reaction during peptidoglycan synthesis. They are broad spectrum drugs frequently given to patients with penicillin allergies. Most cephalosporins (including cephalothin, cefoxitin, ceftriaxone and cefoperazone) are administered parenterally.

Tetracyclines:

These are a family of antibiotics with a common four-ring structure to which a variety of side chains are attached. Naturally produced tetracyclines, oxytetracycline and chlorotetracycline are produced by some species of the actinomycete genus Streptomyces; others are semi synthetic drugs. These antibiotics inhibit protein synthesis by combining with the small (30S) subunit of the ribosome and inhibiting the binding of aminoacyl-tRNA molecules to the ribosomal A site. These are broad spectrum antibiotics active against gram-negative, gram-positive bacteria, rickettsias, Chlamydia.

Aminoglycoside antibiotics:

Streptomycin, kanamycin, neomycin and tobramycin are synthesized by Streptomyces, whereas gentamicin comes from a related bacterium, Micromonospora purpurea. Aminoglycosides bind to the small ribosomal subunit and interfere with protein synthesis and also cause misreading of the genetic message carried by mRNA. These antibiotics are most active gram-negative pathogens, but they are quite toxic and can cause deafness, renal damage, loss of damage, nausea and allergic responses.

Erythromycin (Macrolides):

Erythromycin is synthesized by Streptomyces erythraeus and is usually bacteriostatic, braod spectrum and binds with the 23S rRNA of the 50S ribosomal subunit to inhibit peptide chain elongation during protein synthesis. The other macrolides, Clindamycin is effective against a variety of bacteria including Staphylococci and anaerobes such as Bacteroides. Azithromycin is particularly effective against Chlamydia trachomatis .

Vancomycin:

Vancomycin is produced by Streptomyces orientalis and blocks peptidoglycan synthesis by inhibiting the transpeptidation step that cross-links adjacent peptidoglycan strands. It is affective against Staphylococcus and some members of the genera Clostridium, Bacillus, Streptococcus and Enterococcus.

Chloramphenicol:

Mostly made by chemical synthesis and was previously being produced from cultures of Streptomyces venezuelae. It binds to 23S rRNA on the 50S ribosomal subunit and inhibits the peptidyl transferase and is bacteriostatic. It is a broad spectrum antibiotic but is quite toxic and the common side effect is a temporary or permanent depression of bone marrow function, leading to aplastic anemia and a decreased number of blood leukocytes.