Antibiotics affecting peptidoglycan

Intrinsic Activity. y3-Lactam antibiotics affect sensitive bacteria by inhibiting late stages in tire biosynthesis of their cell wall peptidoglycan. 

P-Lactam antibiotics show their lethal effect by inhibiting the synthesis of bacterial peptidoglycan, thereby disrupting the cell morphology and eventually resulting in cell lysis and death. Because the antibacterial effect of P-lactam is affected by the permeability of the outer membrane of bacteria, it is important in the evaluation of drug efficiency... 

A) Oral bioavailability is affected by first-pass hepatic metabolism Only third-generation cephalosporins cross the blood-brain barrier Procaine penicillin G is the most commonly used intravenous form of the antibiotic Renal tubular reabsorption of beta-lactams is inhibited by probenecid Nafcillin and ceftriaxone are eliminated mainly via biliary secretion The mechanism of antibacterial action of cephalosporins involves (A) Inhibition of the synthesis of precursors of peptidoglycans Interference with the synthesis of ergosterol Inhibition of transpeptidation reactions Inhibition of beta-lactamases Binding to cytoplasmic receptor proteins... 

Penicillins and cephalosporins specifically inhibit late stages of the enzymatic construction of the bacterial peptidoglycan cell wall component, a network of peptides and polysaccharides. Since mammalian cells do not possess such a cell wall, the jS-lactam antibiotics are very specific and virtually non-toxic. This ideal property is not shared by other bactericidal substances, which impair or prevent growth of microorganisms by other, less specific, reaction mechanisms. This is true, e.g. for compounds affecting ion transport in lipid membranes. 

When bacteria are exposed to 3-lactams a small amount of the antibiotic becomes covalently linked to the cells. The amount bound varies with the nature of the organism and the antibiotic but it is always very low, of the order of 200-4000 molecules per cell. These covalently tound molecules are responsible for damaging and, ultimately, killing the cell. They are bound to transpeptidases and carboxypeptidases and effectively inhibit the enzymes. Since no other metabolic or biosynthetic activities are affected the cells continue to grow but are unable to produce cross-linked peptidoglycan. Abnormal cell shapes develop and the cells eventually stop growing. The precise fate of the cells depends upon the nature and the concentration of the 3"lactam involved and upon the organism itself. Lysis is a common phenomenon but filaments and cells with other unusual shapes can persist without lysis. 

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