Bacteria can develop resistance to antibiotics through multiple mechanisms. These involve structural changes (cell wall, ribosomes, DNA), enzymatic modification or cleavage of drugs, and altered metabolic pathways. Understanding these mechanisms is critical for Step 1, as it explains why certain antibiotics fail and guides clinical treatment choices.
Major Mechanisms of Resistance
| Target / Mechanism | Examples of Resistance | Drugs Affected |
|---|---|---|
| Drug cleavage (enzymatic inactivation) | β-lactamase (penicillinase) breaks β-lactam ring | Penicillin G, V; penicillinase-sensitive penicillins; cephalosporins; carbapenems |
| Drug modification (enzymatic inactivation) | Enzyme-mediated modification of antibiotics | Aminoglycosides, chloramphenicol |
| Altered target (ribosome / rRNA binding site mutation) | Resistance via rRNA or ribosomal protein changes | Linezolid, macrolides |
| Altered cell wall structure | Decreased drug uptake or altered binding sites | Penicillinase-resistant penicillins, cephalosporins |
| Altered enzyme / metabolic pathway | The mutation of the target enzyme reduces drug binding | Sulfonamides, fluoroquinolones |
Key Point
- Enzymatic inactivation (e.g., β-lactamases, aminoglycoside-modifying enzymes) is a major mechanism of resistance.
- Target modification (ribosomal or enzymatic changes) prevents antibiotic binding.
- Altered permeability/uptake and efflux pumps also play important roles (e.g., in tetracycline and fluoroquinolone resistance).
Learning Objective: Be able to identify the main mechanisms of antibiotic resistance, match them to the drug classes they inactivate, and recognize their clinical significance in antibiotic failure.
