Amoxicillin and ampicillin These drugs are more active against Enterococci Certain gram-negative bacilli, such as non-beta-lactamase-producing H influenzae, E coli, and Proteus mirabilis; Salmonella species; and Shigella species The addition of a beta-lactamase inhibitor (clavulanate or sulbactam) allows use against methicillin-sensitive staphylococci, H influenzae, Moraxella catarrhalis, Bacteroides species, E coli, and K pneumoniae.