Cephalexin, the active ingredient in Keflex, is a beta-lactam antibiotic. It works by inhibiting bacterial cell wall synthesis. Specifically, it binds to penicillin-binding proteins (PBPs) located within the bacterial cell membrane. This binding prevents the formation of peptidoglycan cross-links, a crucial component of bacterial cell walls.
Impact on Bacterial Cell Walls
Without proper peptidoglycan cross-linking, the bacterial cell wall weakens. This compromised structure leads to bacterial cell lysis (rupture) and ultimately, bacterial death. Cephalexin is bactericidal, meaning it directly kills bacteria, rather than simply inhibiting their growth.
Spectrum of Activity
Cephalexin effectively targets gram-positive bacteria, such as Staphylococcus aureus (including some penicillinase-producing strains) and Streptococcus pyogenes. Its activity against gram-negative bacteria is more limited, primarily affecting some strains of E. coli and Proteus mirabilis. Therefore, susceptibility testing is recommended to guide treatment choices.
