2009-07-29

Ampicillin inhibits cell wall biosynthesis. Cleavage of the B-lactam ring by B-lactamase (bla gene) is the mode of resistence.

Chloramphenicol inhibits translation of the 50S ribosomal subunit at the peptidyltransferase step (elongation inhibition). Acetylation by chloramphenicol acetylgtransferase (cat gne) is the mode of resistence.

Kanamycin binds to 70S ribosomal subunit, inhibits translocation and elicits miscoding. Aminoglycoside modifying enzymes (acetyltransferase, phophotransferase and nucleotidyltransferase) alter the antibiotic, preventing its interaction with ribosomes and inactivation it.

Streptomycin inhibits protein synthesis. It binds to the S12 protein of the 30S ribosomal subunit, causing misreading or inhibiting initiation. Mutation in the rpsL (gene for S12 ribosomal protein) prevents binding of streptomycin to the ribosome. Aminoglycoside phosphotransferase also inactiviates this antibiotic.

Tetracycline inhibits protein synthesis (elongation) by preventing binding of aminoacyl-tRNA to the ribosome. Loss of cell wall permeability is the mode of resistance.