Ampicillin is an aminopenicillin that inhibits bacterial cell wall synthesis and achieves synergy with aminoglycosides against select pathogens.
Ampicillin binds penicillin-binding proteins (PBPs) to block peptidoglycan cross-linking, producing time-dependent bactericidal effects. Its positively charged amino group improves Gram-negative penetration compared with natural penicillins. Prolonged exposure above the MIC is crucial; when combined with gentamicin, ampicillin facilitates gentamicin entry into Enterococcus and Listeria cells, resulting in synergistic killing.