Antimicrobials that affect the synthesis and conformation of nucleic acids.

Several antimicrobials act by inhibiting the synthesis of nucleic acids (rifamycins, sulfamides, diaminopyridines), modifying their conformation (quinolones, coumarins) or causing irreversible lesions (nitroimidazoles, nitrofurans). The resistance mechanisms are: a reduction in intracytoplasmic accumulation, modification of the target or the production of a new low-affinity target and, more rarely, enzyme inactivation. Although the mechanisms affecting the targets are specific to each family and can lead to high-level resistance, the reduced permeability of the membrane and the increased efflux are non-specific and result in low-level cross-resistance between several families. The genetic mediation is usually chromosomal for rifamycins and quinolones, although plasmid-mediated resistant genes have been observed. On the other hand, for sulfamides and trimethoprim, plasmid-borne genes are frequent. Resistance to nitroimidazoles and nitrofurans is still not widely understood.