6-Acetylmethylenepenicillanic acid (Ro 15-1903), a potent .BETA.-lactamase inhibitor. II. Antibacterial properties.

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Abstract
The .beta.-lactamase inhibitor Ro 15-1903 showed low affinity for penicillin binding proteins (PBP) of Escherichia coli. When used as a single compound, it displayed no substantial antibacterial activity, but, in combination with ampicillin, was similar to clavulanic acid in conferring activity against ampicillin-resistant strains. Some synergy between Ro 15-193 and piperacillin was found against high inocula of Pseudomonas aeruginosa. Ro 15-1903 markedly enhanced the activity of ceftriaxone against Bacteroides fragilis. In keeping with the in vitro findings, the combination Ro 15-1903 and ampicillin protected mice against systemic infections with .beta.-lactamase-producing strains of Staphylococcus aureus, Klebsiella pneumoniae and Proteus sp., but not against those with Enterobacter cloacae, Serratia marcescens and E. coli producing chromosomally mediated .beta.-lactamase of type I or plasmid-mediated .beta.-lactamase of type TEM.