FIGURE 1.

Schematic representation of different antibiotic resistance mechanisms in bacteria, shown with examples. (A) Antibiotic modification involves the addition of acetyl, phosphate, or adenyl groups to aminoglycosides by N-acetyl transferases (AAC), O-phosphotransferases (APH), and O-adenyltransferases (ANT). Other examples include chloramphenicol acetyl transferases (CAT) and bleomycin N-acetyltransferases (BlmB). (B) Antibiotic degradation is observed with β-lactamases, which hydrolyze the antibiotic. (C) Antibiotic efflux pumps remove the antibiotic from the cell using energy from ATP hydrolysis in ABC pumps like DrrAB, OtrC, TlrC, and MlbYZ, or proton gradients in MFS, MATE, SMR, and RND family pumps. (D) Target modification includes various target alterations, such as 23S rRNA or 16S rRNA methylation, alterations in the peptidoglycan precursors (for example, in the case of glycopeptides), or synthesis of alternate low-affinity targets (PBPs) that reduce or completely block antibiotic (penicillins) from associating with the target. (E) Antibiotic sequestration involves proteins that can associate with the antibiotic and block them from reaching their targets. (F) Target bypass involves generation of additional antibiotic targets or subunits that are not susceptible to binding of the antibiotic. Meth, methylation.