(5) Saturating the drug by increasing the level of the inhibited enzyme.
(6) Production of inhibitor antagonistic metabolite.
(7) Decreasing the metabolic requirement of the cell for the pathway or reaction inhibited by the drug.
Mechanisms (1), (2), (5) and (7) can be achieved by point mutations in chromosome structure or by regulatory genes. For many antibiotitics, however, mechanisms (3), (4) or (6) are unlikely to arise by simple mutation of chromosomal genes. Mechanisms (5), (6) and (7) are not known to occur presently.
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