Practice question

Glycopeptide antibiotics exhibit true bactericidal killing activity rather than simple growth arrest, a distinction critical for treating severe Gram-positive infections. Vancomycin functions by recognizing and binding with high affinity to the D-alanyl-D-alanine dipeptide terminus of the peptidoglycan precursor lipid II that is exposed on the outer face of the cytoplasmic membrane after flipping from the cytoplasm. This binding creates a large steric cap that prevents transglycosylases from polymerizing the alternating N-acetylglucosamine and N-acetylmuramic acid glycan chain and simultaneously blocks transpeptidases, the penicillin-binding proteins, from forming peptide cross-links between stems. Without cross-linking, the nascent peptidoglycan mesh in Gram-positive organisms with 20-80 nm thick wall remains mechanically weak and cannot withstand internal turgor pressures of 20 atmospheres, leading to activation of autolysins and osmotic lysis. Tetracycline, erythromycin and clindamycin bind reversibly to bacterial ribosomes, pausing translation temporarily and causing bacteriostatic arrest where cells resume growth after drug removal, explaining clinical preference for vancomycin in MRSA bacteremia and endocarditis where rapid killing is desired.