An antibiotic is a compound which inhibits the growth of bacteria (bacteriostatic effect) or destroys them (bactericidal effect). The antibiotic effect can be obtained by different mechanisms of which damage of the microbial DNA.
The fact that antibiotics, generally well tolerated, can damage DNA can appear surprising. This discordance between a good tolerance and a mechanism of action, in theory aggressive, is explained by the following facts:
- Certain antibiotics are not toxic by themselves, but only after conversion into toxic derivatives by enzymes present in microorganisms and not in human cells.
- There are many differences between bacterial and human chromosomes. The human chromosomes are separated from the cytoplasm by a nuclear membrane, they are much condensed and are linked to basic proteins, called histones, which could protect them.
- The human topoisomerase II is different from the bacterial topoisomerase II, particularly by the number of subunits.
One can distinguish, schematically, among antibiotics studied here those which carry a nitrate group able to be reduced, nitrofurans and nitroimidazole, and those which inhibit topoisomerase II like quinolones and fluoroquinolones.