1. Inhibition of Peptidoglycan Synthesis: The bacterial cell wall is primarily composed of peptidoglycan, a polymer made up of alternating units of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). The synthesis of peptidoglycan involves several steps, including the production of precursors, polymerization of these precursors, and cross-linking of the polymer strands. Blocking any of these steps can disrupt cell wall formation.
- β-Lactam Antibiotics: Antibiotics such as penicillin and cephalosporins inhibit the transpeptidation reaction, which is crucial for cross-linking peptidoglycan strands. This leads to a weakened cell wall that can't withstand the internal turgor pressure of the cell, resulting in cell lysis.
- Glycopeptide Antibiotics: Antibiotics like vancomycin interfere with the polymerization of peptidoglycan precursors by binding to the D-Ala-D-Ala terminus of the NAM molecule. This prevents the addition of new NAG-NAM units to the growing peptidoglycan chain.
2. Disruption of Cell Wall Integrity: Certain antimicrobial agents can directly damage the existing cell wall, leading to its weakening or rupture.
- Lysozyme: Lysozyme is an enzyme that can break down the β(1-4) glycosidic bonds between NAG and NAM residues, causing the degradation of the cell wall.
- Daptomycin: Daptomycin is an antibiotic that binds to the cell membrane of bacteria, disrupting its function. This can lead to the leakage of cell contents and ultimately cell death.
3. Inhibition of Cell Wall Biosynthesis: Some antimicrobial agents can interfere with the synthesis of cell wall components.
- Bacitracin: Bacitracin inhibits the dephosphorylation of undecaprenyl pyrophosphate, a lipid carrier involved in the synthesis of peptidoglycan precursors. This disrupts the production of these precursors and consequently affects cell wall formation.
- Fosfomycin: Fosfomycin blocks the synthesis of UDP-N-acetylmuramic acid (UDP-NAM), an essential precursor for peptidoglycan biosynthesis. Without sufficient UDP-NAM, the cell cannot construct new cell walls.
By blocking cell wall formation, these antimicrobial agents prevent the division of bacterial cells, leading to the death or inhibition of bacterial growth. This is the basis for the use of many antibiotics in treating bacterial infections.
