In vitro activity of an oxycephem OCP 9-176 compared with its sulfur analog and other beta-lactams

OCP 9-176 is an oxycephem antibiotic that contains a 2-aminothiazolyl, carboxypropyl side chain at C-7 and a pyridinium thiomethyl group at C-3. OCP 9-176 was generally twofold less active than its sulfur-containing analog ME 1228 against Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Providencia stuartii, Proteus vulgaris, and Serratia marcescens. Activity against Enterobacter cloacae and Citrobacter freundii was equivalent. OCP 9-176 was twofold less active than ME-1228 against Pseudomonas aeruginosa and Acinetobacter species. Activity of the two agents was similar against Staphylococcus aureus and Staphylococcus epidermidis. Although OCP 9-176 inhibited E. coli containing TEM-1 and TEM-2, it was less active than ME-1228. Klebsiella organisms with SHV-1 and K-2 beta-lactamases were inhibited, but TEM-3-containing isolates had MICs of 16 micrograms/ml. OCP 9-176 was minimally hydrolyzed by TEM-1, PSE-1, K-1, and P99, and it was a poor inhibitor of P99. Replacement of sulfur with oxygen does not increase the activity of compounds with sulfopyridinium methyl groups at C-3.