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. Author manuscript; available in PMC: 2024 Jun 27.
Published in final edited form as: Adv Microb Physiol. 2023 Jun 27;83:221–307. doi: 10.1016/bs.ampbs.2023.05.003

Figure 7. Overview of antimicrobial resistance determinants in the cell envelope.

Figure 7.

(left) Expression or upregulation of efflux pumps results in resistance to multiple antibiotic classes. The E. coli tripartite AcrAB-TolC pump depicted here is a typical Resistance-Nodulation-Division (RND) pump that extrudes fluoroquinolones, macrolides, and β-lactams from the periplasm to the extracellular milieu. (center) Soluble β-lactamase enzymes competitively bind β-lactam antibiotics in the periplasm and hydrolyze their essential four membered β-lactam ring, therefore preventing inhibition of peptidoglycan synthesis. (right) During LPS synthesis, the phosphate moieties (small yellow circles) of lipid A (black ovals) are modified by mobile colistin resistance (MCR) proteins (phosphoethanolamine addition is depicted by red circles on the lipid A component). This, in turn, reduces the overall charge of the outer membrane and obstructs the activity of last-line polymyxin antibiotics. OM, outer membrane; PM, plasma membrane.