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Antibiotics: Mechanisms of Action and Resistance

Mechanisms of Antibiotic Resistance

Mechanism Example

Inactivation -lactamase

Chloramphenicol acetyltransferase

aminoglycoside modifiers

Mutation of target Penicillin binding proteins

Change in target regulation Dihydrofolate reductase

Decrease in access Porins Pumps

Penicillins

Mechanism of Bactericidal Activity

Interfere with cell wall synthesis by inhibiting various enzymes which catalyze peptidoglycan synthesis

Activity depends upon binding to these target enzymes - penicillin-binding proteins

Resistance Mechanisms

-lactamase inactivation of the B-lactam rin9 B-lactamase inhibitors bind irreversibly to some B-lactamases

Alterations in penicillin-binding-proteins

Cephalosporins

Mechanism of Bactericidal Activity

Similar to penicillin

Mechanisms

B-lactamases

Decreased penetration through porins

Alterations in penicillin binding proteins

-Lactamases in Bacterial Resistance

General Principles

Mechanism of Action

Serine ester leading to hydrolysis of B-lactam ring - most common

Zinc ions disrupt -lactam ring - metallo-enzymes

General Location

Plasmid mediated - facilitates spread

commonest In enterobacteria is TEM-1

Chromosomal Location - ubiquitous In enterobacteria. Expression may be Inducible, high-level constitutive or