What is the mechanism of action of the beta-lactam antibiotic cephalexin?

Cephalexin, a beta-lactam antibiotic, exerts its therapeutic effects primarily by disrupting bacterial cell wall synthesis. Beta-lactam antibiotics, including cephalexin, bind to penicillin-binding proteins (PBPs) located within the bacterial cell wall. This binding inhibits the transpeptidation enzyme, which is crucial for cross-linking peptidoglycan layers in the bacterial cell wall.

The weakening of the cell wall integrity leads to lysis of the bacterial cell, as the osmotic pressure from within the bacteria can no longer be contained. As a result, cephalexin is particularly effective against gram-positive bacteria and certain gram-negative bacteria that possess a cell wall structure dependent on peptidoglycan.

In contrast, the other answer choices represent mechanisms associated with different classes of antibiotics. For instance, the inhibition of protein synthesis occurs with drugs like tetracyclines and macrolides, interference with DNA gyrase is characteristic of fluoroquinolones, and increased cell membrane permeability is typically observed with antibiotics like polymyxins. Thus, the specific action of cephalexin in disrupting cell wall synthesis is the reason why it is effective as an antibiotic.