12.1E: Antibiotic Classifications
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Learning Objectives
Compare the two classes of antibiotics: bactericidal and bacteriostatic antibiotic
Antibiotics can be divided into two classes based on their mechanism of action. Bactericidal antibiotics kill bacteria; bacteriostatic antibiotics inhibit their growth or reproduction.
One way that bactericidal antibodies kill bacteria is by inhibiting cell wall synthesis. Examples include the Beta-lactam antibiotics (penicillin derivatives (penams) ), cephalosporins (cephems), monobactams, and carbapenems) and vancomycin. Other ways that bactericidal antibiotics kill bacteria include inhibiting bacterial enzymes or protein translation. Other batericidal agents include daptomycin, fluoroquinolones, metronidazole, nitrofurantoin, co-trimoxazole and telithromycin. Aminoglycosidic antibiotics are usually considered bactericidal, although they may be bacteriostatic with some organisms. The MBC (minimum bactericidal concentration) is the minimum concentration of drug which can kill 99.99% of the population.
Bacteriostatic antibiotics limit the growth of bacteria by interfering with bacterial protein production, DNA replication, or other aspects of bacterial cellular metabolism. This group includes: tetracyclines, sulfonamides, spectinomycin, trimethoprim, chloramphenicol, macrolides and lincosamides. They must work together with the immune system to remove the microorganisms from the body. However, there is not always a precise distinction between them and bactericidal antibiotics. High concentrations of some bacteriostatic agents are also bactericidal. The MIC (minimum inhibitory concentration) is the minimum concentration of drug which can inhibit the growth of the microorganism.
Further categorization is based on their target specificity. “Narrow-spectrum” antibacterial antibiotics target specific types of bacteria, such as Gram-negative or Gram-positive bacteria, whereas broad-spectrum antibiotics affect a wide range of bacteria, usually both gram positive and gram negative cells. Following a 40-year hiatus in discovering new classes of antibacterial compounds, three new classes of antibacterial antibiotics have been brought into clinical use: cyclic lipopeptides (such as daptomycin), glycylcyclines (such as tigecycline), and oxazolidinones (such as linezolid).
Key Points
- Bactericidal antibodies inhibit cell wall synthesis.
- Bacteriostatic antibiotics limit the growth of bacteria by interfering with bacterial protein production, DNA replication, or other aspects of bacterial cellular metabolism.
- Bacteriostatic antibiotics must work together with the immune system to remove the microorganisms from the body.
Key Terms
- bactericidal : An agent that kills bacteria.
- bacteriostatic : A drug that prevents bacterial growth and reproduction but does not necessarily kill them. When it is removed from the environment the bacteria start growing again.
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