Inhibition of Cell Wall Synthesis

Inhibition of Cell Wall Synthesis , Inhibition of Protein Synthesis, Alteration of Cell Membranes, Inhibition of Nucleic Acid Synthesis ,Antimetabolite Activity ,Mechanisms of Antibiotic Action and Resistance Inhibition of Cell Wall Synthesis (most common mechanism) Inhibition of Protein Synthesis (Translation) (second largest class) Alteration of Cell Membranes Inhibition of Nucleic Acid Synthesis Antimetabolite ActivityThe most common mode of action for antibiotics is the inhibition of cell wall synthesis. Antibiotics that inhibit cell wall synthesis work because of the fact that most eubacteria have peptidoglycan-based cell walls but mammals do not. Growth is prevented by inhibiting peptidoglycan synthesis. Thus these antibiotics only work for actively growing bacteria. The cell wall of new bacteria that grew in the presence of cell-wall-synthesis inhibitors is deprived of peptidoglycan. These bacteria will be subjected to osmotic lysis.

In addition, gram-negative bacteria generally are less susceptible to inhibitors of cell wall synthesis than are gram-positive bacteria. In the former cell wall synthesis inhibitors fail to reach the cell wall because they are blocked by the gram-negative outer membrane

Penicillin is the classic example of an inhibitor of cell wall synthesis. Other examples include: ampicillin, bacitracin, carbapenems, cephalosporin, methicillin, oxacillin and vancomycin

Mechanisms of Resistance

Beta-Lactams: Inhibition of peptidoglycan synthesis (bactericidal)

Resistance occurs when the antibiotic:

  • fails to cross membrane (gram negatives)
  • fails to bind to altered Pennicillin Binding Protein
  • is hydrolysis by beta-lactamases

Vancomycin: Disrupts peptidoglycan cross-linkage

Resistance occurs when:

the antibiotic fails to cross gram negative outer membrane (too large)

the bacterium is intrinsically resistant (pentapeptide terminus)

Bacitracin: Disrupts movement of peptidoglycan precursors (topical use)

Resistance occurs when the antibiotic fails to penetrate into cell

Antimycobacterial agents: Disrupt mycolic acid or arabinoglycan synthesis (bactericidal)

Resistance occurs when there is a reduced uptake and/or when the antibacterial target sites are altered.

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Mechanisms of Antibiotic Action and Resistance