In-vitro activity of the new penems FCE 22101 and FCE 24362 alone or in combination with aminoglycosides against streptococci isolated from patients with endocarditis.

Seven strains of viridans streptococci isolated from patients with endocarditis were inhibited in vitro by 0.06-2 mg/l and 0.016-0.5 mg/l of the penems FCE 22101 and FCE 24362 respectively. The MBCs were the same or two-fold higher than the respective MIC with three exceptions. One strain of Streptococcus faecalis was only inhibited (8 mg/ml respectively 0.5 mg/l; MBC greater than 32 mg/l) and one strain of Str. faecium was resistant (MIC greater than or equal to 16 mg/l). When combined with gentamicin or netilmicin a bactericidal and synergistic killing was observed within 1-8 h in all strains except Str. faecium. Synergy could also be confirmed in all cases by following bacterial growth kinetics after elimination of antibiotics, by calculating the difference between the times required for bacteria exposed to antibiotic and unexposed bacteria to increase in numbers (PAE).