[In vitro activity of linezolid/ertapenem combination in resistant gram-positive bacteria]

The increasing prevalence of vancomycin-resistant enterococcus and methicillin-resistant staphylococcus infections has become a major therapeutic challenge and alternative therapy options are under consideration. In the present study, we aimed to evaluate the in vitro antibacterial activity of linezolid combined with ertapenem against two vancomycin-resistant Enterococcus faecium (VREF), two methicillin-resistant Staphylococcus aureus (MRSA) and two methicillin-resistant Staphylococcus epidermidis (MRSE) strains isolated from clinical specimens. In vitro activity of linezolid/ertapenem combination at 1/2 x MIC (minimal Inhibitory Concentration), 1 x MIC and 4 x MIC concentrations for each of the isolates was determined by time-kill curve method. At 1 x MIC and 4 x MIC concentrations, additive effect was detected for MRSA (at 6 and 24 h) and VREF (at 6 h) strains. Synergism was observed between two antibiotics at 4 x MIC concentration against one of the MRSE strains at 6th hour. Additive effect was determined at 6th and 24th hours in this strain at 1 x MIC concentration. No synergism was present in the other MRSE strain but additive interaction was detected at 6 h (1/2 x MIC) and 24 h (1 x MIC). Although these results support the use of linezolid/ertapenem combination in infections caused by resistant gram-positive strains, further in vitro and in vivo studies are necessary.