Saturated fatty acids enhance daptomycin activity in a Fak-dependent manner in enterococci

Antibiotic resistance of Gram-positive bacteria poses a major clinical challenge. Daptomycin, a lipopeptide antibiotic, is a treatment option for drug-resistant organisms. However, there have been clinical reports of daptomycin resistance and in vitro reports of daptomycin tolerance that can result in treatment failure. Daptomycin possesses a fatty acid tail that inserts into the membrane, and membrane fatty acid content can influence its binding. Given that, we examined the potential of fatty acids to enhance daptomycin activity against enterococcal strains. We demonstrate that the saturated fatty acids myristic and palmitic acids increase bacterial susceptibility to the antibiotic, even for a daptomycin-resistant clinical isolate. These effects were highly specific with no impact on daptomycin susceptibility of Staphylococcus aureus . Growth of enterococci with myristic or palmitic acid reduced membrane fluidity, potentially promoting tighter daptomycin insertion. However, we noted no difference in membrane permeability for cells treated with fatty acids and daptomycin. While cells exposed to saturated fatty acids experience greater membrane depolarization, the lack of consistent, significant time-dependent changes upon daptomycin treatment suggests that depolarization alone does not fully explain the increased sensitivity. A strain that is unable to incorporate exogenous fatty acids into phospholipids was insensitive to the effects of saturated fatty acids on its susceptibility to daptomycin, highlighting the necessity of fatty acid incorporation onto lipid headgroups for potentiation. Overall, our data suggest that the incorporation of specific saturated fatty acids within the enterococcal membrane likely disrupts lipid composition, membrane organization and cellular envelope homeostasis, ultimately contributing to enhanced daptomycin susceptibility.