A new pencillin with anti-klebsiella activity: 3-(5-tetrazolyl) penam.

The in vitro activity of a new semi-synthetic penicillin, CP-35,587, 3-(5-tetrazolyl) penam, was investigated against 496 clinical isolates of gram-negative bacilli and 113 clinical isolates of gram-positive cocci. All of the gram-positive cocci were sensitive to CP-35,587 except penicillin G resistant isolates of Staphylococcus aureus. This antibiotic inhibited a majority of isolates of Escherichia coli, Klebsiella spp. and Proteus mirabilis at a concentration of 6.25 microgram/ml. Also, approximately half of the isolates of Serratia marcescens and Enterobacter spp. were inhibited at a concentration of 12.5 microgram/ml. CP-35,587 was inactive when high concentrations of organisms were used as inocula. CP-35,587 was more active than mezlocillin, azlocillin, amoxicillin, ticarcillin and carbenicillin against isolates of K. pneumoniae, but other penicillins were more acte than CP-35,587 against other species of gram-negative bacilli.