Resistance of the Enterobacteriaceae to antibiotics, especially of the β lactam type, is
increasingly dominated by the mobilization of continuously expressed single genes that
encode efficient drug modifying enzymes. Strong and ubiquitous selection pressure has
seemingly been accompanied by a shift from “natural” resistance, such as inducible
chromosomal enzymes, membrane impermeability, and drug efflux, to the modern paradigm
of mobile gene pools that largely determine the epidemiology of modern antibiotic …