Which of the following is the mechanism of action of this antibiotic in this patient? A 2-year old girl takes oral cephalexin for treatment of Impetigo caused by group A beta-hemolytic Streptococcus.
A. Binding to bacterial 30S ribosomal subunits B. Binding to bacterial 50S ribosomal subunits C. Inhibition of bacterial dihydrofolate reductase D. Interference with bacterial cell wall synthesis E. Production of beta-lactamase
Mechanism of the antibacterial effect
- It is due mainly to the two following actions:
1) Beta-lactam antibiotics bind to specific beta-lactam receptors called penicillin-binding proteins (PBPs) located on the cytoplasmic membrane. These proteins are enzymes endowed with various catalytic functions which are inhibited by the binding with the
antibiotic. The most important enzymes inhibited are transpeptidases which catalyze the
final cross-link step in the synthesis of murein (also called peptidoglycan ). Since peptidoglycan layers are constituents of bacteria cell wall, the synthesis of this wall is blocked.
2) Autolytic enzymes (called autolysins or murein hydrolases) are present in the cell wall and degrade the peptidoglycan. Beta-lactam antibiotics can activate these autolysins (apparently by blocking an autolysin inhibitor) so promoting the lysis of bacteria.