Table 2.
Summary of antibiotic resistance mechanisms in important Gram-positive bacteria.
| Antibiotic Class | S. aureus | Enterococcus spp. |
|---|---|---|
| Penicillins | Penicillinase, production of PBP2a | Low affinity PBPs |
| Cephalosporins 1st gen. | PBP2a | Low affinity PBPs |
| Cephalosporins 2nd gen. | PBP2a | Low affinity PBPs |
| Cephalosporins 3rd gen. | PBP2a | Low affinity PBPs |
| Cephalosporins 4th gen. | PBP2a | Low affinity PBPs |
| b-lactamase inhibitors | PBP2a | |
| Carbapenems | Development of PBP2a | Low affinity PBPs |
| Tetracyclines | Ribosomal methylation of binding sites, efflux pumps | Ribosomal methylation of binding sites, efflux pumps |
| Tigecyclines | Efflux pumps | Ribosomal methylation of binding sites, efflux pumps |
| Macrolides and clindamycin | Ribosomal methylation of binding sites, efflux pumps | Efflux pumps, clindamycin inactivating enzymes |
| Fluoroquinolones | Mutations in topoisomerase IV and DNA gyrase, efflux pumps | Mutations in topoisomerase IV and DNA gyrase, production of protection proteins |
| Rifampicin | Mutations in RNA polymerase gene | Mutations in RNA polymerase gene |
| TMP/SMX | Mutations in DHPS and DHFR | Folate absorption from environment |
| Aminoglycosides | Aminoglycoside degradation enzymes | Aminoglycoside degradation enzymes, ribosomal mutations |
| Daptomycin | Electrostatic repulsion through increase to the cell-surface charge |
E faeccium: electrostatic repulsion through increase to the cell-surface charge. E. faecalis: redistribution of cardiolipin away from septum plane |
| Vancomycin | VRSA: altered structure of peptidoglycan precursors from D-Ala-D-Ala to D-Ala-D-Lac; VISA: increased production of peptidoglycan, thicker cell wall, decoy D-Ala-D-Ala dipeptides on cell surface | Altered structure of peptidoglycan precursors from D-Ala-D-Ala to D-Ala-D-Lac |
| Linezolid | Mutations to the 23S rRNA, altering required modifications to the 23S rRNA, mutations to the 50S ribosomal L3 protein | Mutations to the 23S rRNA |
Abbreviations: PBP, penicillin binding protein; TMP/SMX, trimethoprim-sulfamethoxazole; DHPS, dihydropteroate synthase; DHFR, dihydrofolate reductase.