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Mechanism Example
Inactivation ß-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
ß-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
General Principles
Mechanism of Action
Serine ester leading to hydrolysis of B-lactam ring - most common
Zinc ions disrupt ß-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