Synergy and cumulated killing effect of the penems FCE 22101 and FCE 25199 in combination with gentamicin against bacteria isolated from septicaemia.

Blood isolates of Enterococcus faecalis, Streptococcus sanguis, Staphylococcus aureus, E. coli and Klebsiella oxytoca were tested for their synergistic and cumulated killing effect (CKE) with the new penems FCE 22101 or FCE 25199 in combination with gentamicin. The tissue cage model in rabbits was used to study the CKE in vivo after antibiotic treatment of the bacteria in vitro. Synergy was observed within two to seven h with all isolates in early logarithmic phase, except with S. aureus, which was rapidly killed by the penems alone. After one h treatment with the antibiotic combinations in vitro, a CKE was demonstrated for up to six h both in vitro and in vivo. The magnitude of the CKE differed between strains and in vitro vs. in vivo.