The in vitro activity of a new semisynthetic penicillin, piperacillin, was determined against 577 clinical isolates of gram-positive cocci and gram-negative bacilli. A concentration of 12.5 mug/ml inhibited 92% of isolates of Pseudomonas aeruginosa, 82% of Serratia marcescens, 73% of Escherichia coli, 61% of Klebsiella spp., and 42% of Enterobacter spp. Most Proteus spp. were extremely suscepti...
