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