IN-VITRO STUDY OF THE SYNERGY BETWEEN BETA-LACTAM ANTIBIOTICS AND GLYCOPEPTIDES AGAINST ENTEROCOCCI

The synergy between glycopeptides and beta-lactams was studied using d ifferent techniques such as broth macrodilution, killing curves and ag ar dilution combined with agar diffusion. Two glycopeptide-resistant e nterococci isolated from different clinical samples were used. Results showed different effects with significant changes in MICs. Antibacter ial activity was related to the concentration of glycopeptide and beta -lactam for Enterococcus faecalis 8253, while for Enterococcus faecium 8072 a paradoxical effect was observed. With this strain, the best sy nergic effect was detected at teicoplanin concentrations of 1-4 mg/L, but antibacterial activity was reduced at concentrations of 8, 16 and 32 mg/L. No synergic effect was observed with vancomycin. The combinat ion of agar dilution with agar diffusion techniques may constitute a s imple method for routine detection of synergic effects between glycope ptides and beta-lactams.