18.01.5 Inhibitors of DNA Synthesis

An example of an antibiotic that inhibits the DNA synthesis in bacteria is trimethoprim. Trimethoprim is classified as a folate inhibitor. Trimethoprim inhibits the enzyme dihydrofolate reductase, by competing with folic acid for the enzyme (Figure 18.3). Dihydrofolate reductase is necessary to promote the incorporation of folic acid into DNA. When this enzyme is inhibited with trimethoprim, there is reduced production of bacterial DNA, which stops the bacteria from undergoing binary fission.

Figure 18.3 Mechanism of action of trimethoprim (Copyright Sheila Doggrell, QUT)

Trimethoprim is bacteriostatic. Thus, it halts the division of existing bacterial, but does not kill the existing bacteria. Hopefully, the immune system will deal with the remaining bacteria. Trimethoprim is used orally, mainly to treat urinary tract infections.