Ampicillin is a broad-spectrum, semi-synthetic beta-lactam antibiotic. The 2-amino-2-phenylacetamido group substituent at position 6 of the penam ring confers activity against Gram-negative bacteria, including Escherichia coli, Haemophilus influenzae, Salmonella Typhi and Shigella. Ampicillin binds to and inactivates penicillin-binding proteins located on the inner membrane of the bacterial cell wall. Inactivation of PBPs interferes with the cross-linkage of peptidoglycan chains necessary for bacterial cell wall strength and rigidity, interrupting bacterial cell wall synthesis and resulting in the weakening of the bacterial cell wall and cell lysis.