Lipopeptide Laur-CKK-NH2 dimer preserves daptomycin susceptibility and enhances its activity against Enterococcus faecalis

An experimental study was performed to evaluate both in vitro and in vivo the kind of interaction between the Laur-CKK-NH2 dimer and daptomycin using two Enterococcus faecalis strains with different patterns of susceptibilities. We evaluated whether selection for daptomycin-resistant E. faecalis could be prevented in vitro by combining daptomycin with the Laur-CKK-NH2 dimer. The strains were serially exposed in broth to 2-fold stepwise increasing concentrations of daptomycin alone or in combination with a fixed concentration (0.25×MIC) of the Laur-CKK-NH2 dimer. We also performed an in vitro synergy study. For in vivo studies, a mouse model of enterococcal sepsis was used. In vitro experiments: exposure to daptomycin alone gradually selected for enterococci with increased MICs; and the Laur-CKK-NH2 dimer showed a positive interaction with daptomycin and was able to prevent the resistance. In vivo experiments: the main outcome measures were lethality and quantitative blood cultures; and the Laur-CKK-NH2 dimer combined with daptomycin exhibited the highest efficacy for all main outcome measurements. These results highlight the potential usefulness of combining daptomycin with the Laur-CKK-NH2 dimer. The combination provides a future therapeutic alternative for the treatment of enterococcal severe infections.