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

Abstract

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/1. Imipenem showed good bactericidal activity against both groups of strains with MBC₅₀/MBO₉₀ values of 1/4 and 4/16 mg/1 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.