Comparative activity of imipenem (N-formimidoyl thienamycin) on enterococci and its interactions with aminoglycosides.

Activity of imipenem (N-formimidoyl thienamycin, ampicillin and vancomycin against 27 Streptococcus faecalis and 5 Str. faecium was determined. Also evaluated were the interactions of imipenem, ampicillin and vancomycin with streptomycin or amikacin or sissomicin. Imipenem showed the most inhibitory activity against Str. faecalis with MIC50 and MIC90 values 0.5 and 2 mg/l respectively, Str. faecium strains were less susceptible to imipenem with MIC50/MIC90 values of 2/16 mg/l. Imipenem showed good bactericidal activity against both groups of strains with MBC50/MBC90 values of 1/4 and 4/16 mg/l respectively. The most favourable interactions (synergy and addition) of imipenem were with streptomycin (72.2%) and sissomicin (53.2%). Combinations containing amikacin were the least favourable. Similar results were obtained with these combinations against Str. faecium.