Modified time-kill assay against multidrug-resistant Enterococcus faecium with novel antimicrobial combinations

This study used a modified time-kill assay to compare the in-vitro activity of chloramphenicol and quinopristin/dalfopristin combined with vancomycin, ampicillin or gentamicin against multidrug-resistant Enterococcus faecium. The assay uses standardized time-kill methods with the following modificat ions: centrifugation of the test tubes at 1-2 h intervals, removal of super natant and resuspension of bacteria in media containing antibiotic concentr ations corresponding to simulated steady-state serum concentrations, None o f the agents, alone or in combination, produced bactericidal or synergic ac tivity. The modified time-kill assay more closely simulates in-vivo conditi ons and may provide a better qualitative assay to determine the interaction between antimicrobial agents and bacteria.