Methicillin sodium salt is a semisynthetic antibiotic belonging to the penicillin class characterized by inhibition of bacterial cell wall synthesis It exerts bactericidal activity by binding covalently to bacterial transpeptidases (penicillin-binding proteins PBPs) disrupting peptidoglycan cross-link formation and compromising cell wall integrity Methicillin has been employed in research primarily against gram-positive bacteria including penicillinase-producing strains such as Staphylococcus aureus Experimentally methicillin can serve as a reference compound in vitro studies evaluating antimicrobial susceptibility or resistance mechanisms The minimum inhibitory concentration (MIC) values reported typically range between 0 5 to 4 g/mL depending upon bacterial strain and experimental conditions Currently its primary use is confined to laboratory research due to availability of alternative penicillin derivatives