1. Pharmacology
        1.5. Antibiotics
            1.5.1. Beta-lactam antibacterial drugs Penicillin

Penicillin group

Types of penicillins


Group characteristics



Bactericidal, by interfere with bacterial cell wall (peptidoglycan) synthesis

Mechanism of action

Intact beta-lactam ring binds to various proteins
--> Binds to transpeptidase and carboxypeptidase
--> Prevents cross-linkage of peptidoglycan
--> Bacterial cell wall weakened


Antibacterial spectrum




Gram-positive cocci has thick peptidoglycan cell wall

When exposed to beta-lactam
--> Growth continue at normal rate (but with reduced cross-linkage)
--> Cell wall becomes weakened
--> Lysis

Release of bacterial cellular component (lipoteichoic acid, a bacterial sugar alcohol phosphate)
--> Accelerate peptidoglycan breakdown
--> Cell death


Rarely results in bacterial killing to the point of extinction

Some sensitive cells (the persistors) will remain dormant until the antibiotic is removed

Extinction is achieved by the addition of a synergistic antibiotics, e.g. aminoglycoside
* Gentamicin can penetrate the cell walls better due to peptidoglycan damage


Gram-negative bacilli

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