Daptomycin is a last-resort membrane-targeting lipopeptide approved for the treatment of drug-resistant staphylococcal infections such as bacteraemia and implant-related infections. Although cases of resistance to this antibiotic are rare, increasing clinical, in vitro and animal studies report treatment failure, notably against Staphylococcus aureus. The aim of this study was to identify the features of daptomycin and its target bacteria that lead to daptomycin treatment failure. We show that daptomycin bactericidal activity against S. aureus to significantly varies with the growth state and strain according to membrane fatty acid composition. Daptomycin efficacy as an antibiotic relies on its ability to oligomerize within membranes and form pores that subsequently lead to cell death. Our findings ascertain that daptomycin interacts with tolerant bacteria and reaches its membrane target, regardless of its functionality. However, the final step of pore formation does not occur in cells that are daptomycin-tolerant, strongly suggesting its incapacity to oligomerize. Importantly, membrane fatty acid contents correlated with poor daptomycin bactericidal activity, which could be manipulated by fatty acid addition. In conclusion, daptomycin failure to treat S. aureus is not due to a lack of antibiotic-target interaction but is driven by its capacity to form pores, which depends on membrane composition. Manipulation of membrane fluidity to restore S. aureus daptomycin bactericidal activity in vivo could open the way to novel strategies of antibiotic treatment.
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