Overview of Antibiotics Inhibiting Cell Wall Synthesis

Overview of Antibiotics Inhibiting Cell Wall Synthesis

• Beta-lactam antibiotics inhibit bacterial cell wall synthesis. Examples include penicillins, cephalosporins, carbapenems, and monobactams.
• Vancomycin is another class of antibiotics that inhibits cell wall synthesis, but it's not a beta-lactam.

Beta-lactam Antibiotics (Penicillins)

• Penicillins are the first discovered antibiotics, classified by their activity spectrum and resistance to beta-lactamases.
• Structure: Crucial for activity are thiazolidine and beta-lactam rings, and variations in the side chain (R-group) influence the penicillin type's activity.
• Natural Penicillin (Penicillin G): Effective against Gram-positive bacteria (like Streptococcus and Staphylococcus), but susceptible to penicillinase (beta-lactamase).
• Semisynthetic Penicillins: Modified to overcome natural penicillin drawbacks (like resistance to beta-lactamase and improved acid stability).
  • Examples include penicillin V (acid-stable, oral use for less severe infections) and penicillinase-resistant penicillins (like methicillin, cloxacillin) designed for penicillinase-producing Staphylococcus species.

Mechanism of Action

• Penicillins inhibit bacterial cell wall synthesis, specifically the final peptidoglycan cross-linking step.
• This leads to bacterial lysis (and death), particularly during active bacterial replication.
• Penicillin resistance occurs due to penicillinase (beta-lactamase) enzymes that destroy the beta-lactam ring; Gram-negative bacteria's outer membrane further impedes treatments. Altered penicillin-binding proteins (PBPs) in bacteria like MRSA also impede treatment.

Cephalosporins

• Cephalosporins are beta-lactam antibiotics, divided into generations.
• 1st generation: Primarily effective against Gram-positive bacteria (e.g., cefazolin, cephalexin).
• Subsequent generations (2nd, 3rd, 4th) exhibit increased activity against Gram-negative bacteria and broader resistance to beta-lactamases, often including resistant strains.

Other Beta-Lactam Antibiotics

• Carbapenems (e.g., Imipenem) are broad-spectrum antibiotics, often combined with cilastatin to prevent renal metabolism.
• Monobactams (e.g., Aztreonam) are primarily active against Gram-negative bacteria, with limited Gram-positive and anaerobic activity.

Vancomycin

• Vancomycin is a glycopeptide antibiotic that inhibits cell wall synthesis by binding to D-alanine-D-alanine portions of peptidoglycan precursors. Primarily used for Gram-positive bacteria, including MRSA.
• It interferes with peptidoglycan cross-linking, leading to weakened cell walls and bacterial lysis (from osmotic pressure).

Penicillin's Spectrum of Activity

• Penicillin G effectively targets Gram-positive cocci (streptococci, pneumococci).
• Staphylococcus aureus has developed resistance.
• Gram-negative cocci (N. gonorrhoeae, N. meningitidis) are susceptible.
• Anaerobic species (like Clostridium species) are highly sensitive.
• Effective against bacilli (e.g., Bacillus anthracis, Corynebacterium diphtheriae)

Penicillin Pharmacokinetics

• Penicillin G is acid-labile and absorbed parenterally (IV/IM).
• Penicillins are mainly excreted by the kidneys.

This quiz explores the mechanisms and classifications of antibiotics that inhibit bacterial cell wall synthesis. Focused primarily on beta-lactam antibiotics such as penicillins and their structural significance, the quiz also covers the role of vancomycin as a non-beta-lactam inhibitor. Test your knowledge about these critical antimicrobial agents.