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Table 1 Examples of clinically relevant resistance mechanisms in major bacterial pathogens

From: Coping with antibiotic resistance: contributions from genomics

Resistance mechanism Molecular basis Antibiotics affected Relevant clinical pathogens
Drug inactivation β-Lactamases β-Lactams (variable spectrum, depending on the enzyme type) Many Gram-positive and Gram-negative pathogens
  Aminoglycoside-modifying enzymes Aminoglycosides (variable spectrum, depending on the enzyme type) Many Gram-positive and Gram-negative pathogens
Target modification Mutated DNA topoisomerases Quinolones and fluoroquinolones Many Gram-positive and Gram-negative pathogens
  Mutated RNA polymerase Rifampin Staphylococcus aureus, Mycobacterium tuberculosis
  Altered peptidoglycan (presence of D-Ala-D-Lac depsipeptide) Glycopeptides Enterococci
Target protection 23S ribosomal RNA methylation by Erm methylases Macrolides Streptococci, Staphylococci, anaerobes
  16S ribosomal RNA methylation by Arm/Rmt-like methylases Aminoglycosides Enterobacteriaceae
  Ribosomal protection by Tet proteins Tetracyclines Many Gram-positive pathogens
  Topoisomerase protection by Qnr proteins Quinolones and fluoroquinolones Enterobacteriaceae
Bypass of target function Production of PBP2a, which takes over the functions of other PBPs Most β-lactams Methicillin-resistant Staphylococcus aureus (MRSA)
Impermeability Loss of OprD porin Carbapenems Pseudomonas aeruginosa
Drug efflux Tet MFS-type pumps Tetracyclines Enterobacteriaceae, Staphylococci
  Upregulation of MexAB RND-type pump Fluoroquinolones and most anti-pseudomonal β-lactams Pseudomonas aeruginosa
  Upregulation of MexXY RND type pump Fluoroquinolones, aminoglycosides, cefepime and meropenem Pseudomonas aeruginosa
  1. PBP: penicillin-binding-protein.