Diversity of the mechanisms of resistance to β-lactam antibiotics

The sensitivity of a bacterium to β-lactam antibiotics depends upon the interplay between 3 independent factors: the sensitivity of the essential penicillin-binding enzyme(s), thee quantity and properties of the β-lactamase(s) and the diffusion barrier that the outer-membrane of Gram-negative bacteria can represent. Those three factors can be modified by mutations or by the horizontal transfer of genes or portions of genes.