Quinolone antibiotics inhibit bacterial growth by affecting

Quinolones block bacterial DNA synthesis by inhibiting DNA gyrase. This introduces negative superhelical turns into duplex DNA, thereby maintaining the negative superhelical tension of the bacterial chromosome during DNA replication. Ciprofloxacin and norfloxacin are active against a broad range of organisms that cause infections of the lower respiratory tract, intestinal tract, urinary tract and soft tissues. The original form, nalidixic acid, is useful only for urinary tract infections. Rifampin directly inhibits bacterial RNA polymerase. The reverse transcriptase of human immunodeficiency virus is inhibited by azidothymidine (AZT). Penicillins and cephalosporins are transpeptidase enzymes that function in the final stages of cell wall synthesis. They are inactivated by f3-lactamase enzymes, which break a single bond in the f3-lactam ring of these antibiotics. Nonclinical useful drugs such as mitomycin C and actinomycin D can directly interfere with DNA polymerase activity, but they are useful only as biochemical tools in experiments.