In vitro and in vivo activity of D-serine in combination with β-lactam antibiotics against methicillin-resistant Staphylococcus aureus

As D-amino acids play important roles in the physiological metabolism of bacteria, combination of D-amino acids with antibiotics may provide synergistic antibacterial activity. The aim of the study was to evaluate in vitro and in vivo activity of D-serine alone and in combination with beta-lactams against methicillin-resistant Staphylococcus aureus (MRSA) strains, and to explore the possible sensitization mechanisms. The activity of D-serine, beta-lactams alone and in combinations was evaluated both in vitro by standard MICs, time-kill curves and checkerboard assays, and in vivo by murine systemic infection model as well as neutropenic thigh infection model. An in vitro synergistic effect was demonstrated with the combination of D-serine and beta-lactams against MRSA standard and clinical strains. Importantly, the combinations enhanced the therapeutic efficacy in the animal models as compared to beta-lactam alone groups. Initial mechanism study suggested possible revision of D-alanine-D-alanine residue to D-alanine-D-serine in peptidoglycan by adding of D-alanine in the medium, which may cause decreased affinity to PBPs during transpeptidation. In conclusion, D-serine had synergistic activity in combination with beta-lactams against MRSA strains both in vitro and in vivo. Considering the relatively good safety of D-serine alone or in combination with beta-lactams, D-serine is worth following up as new anti-MRSA infection strategies. (C) 2019 Chinese Pharmaceutical Association and Institute of Materia Medica, Chinese Academy of Medical Sciences. Production and hosting by Elsevier B.V.