Daptomycin resistance in Enterococcus faecium can be delayed by disruption of the LiaFSR stress response pathway

The LiaFSR signaling pathway plays a major role in mediating daptomycin (DAP) resistance for both Enterococcus faecalis and Enterococcus faecium. LiaFSR inhibition induces DAP hypersusceptibility but could also potentially delay the acquisition of DAP resistance in a combinatorial therapy of DAP with a LiaFSR inhibitor. To evaluate the potential efficacy of this approach, the adaptation to DAP by both E. faecalis and E. faecium lacking a functional LiaFSR were examined. Here, clinical isolates of E. faecium with liaR deletions were evolved to DAP resistance using in vitro experimental evolution. Genomic analysis of resistant populations was used to identify both the alleles and their relative frequencies in driving DAP resistance. Microscopic and biochemical analyses were then employed to investigate how those adaptive alleles contributed to DAP resistance. We found that deletion of liaR from the E. faecium genome significantly delayed the onset of DAP resistance. Unsurprisingly, resistance strategies emerged eventually. These alternative strategies were influenced by both environment and ancestral genome. The delay in the acquisition of DAP resistance when liaR was deleted supports the concept of developing a LiaFSR pathway inhibitor to prolong DAP efficacy against enterococci. The loss of a functional LiaFSR pathway reset the adaptive landscape and forced adaptation to progress in new ways that were slower in providing DAP tolerance. The observed adaptive trajectories were strongly influenced by both the environment and ancestral genome.