Synergistic potential of Leu-teixobactin and cefepime against multidrug-resistant Staphylococcus aureus.

Staphylococcus aureus (S. aureus) is a significant Gram-positive opportunistic pathogen behind many debilitating infections. β-lactam antibiotics are conventionally prescribed for treating S. aureus infections. However, the adaptability of S. aureus in evolving resistance to multiple β-lactams contributed to the persistence and spread of infections, exemplified in the emergence of methicillin-resistant S. aureus (MRSA). In the present study, we investigated the efficacies of the synthetic teixobactin analogue, Leu-teixobactin, combined with the penicillinase-resistant cephalosporin cefepime against MRSA strains. The Leu-teixobactin and cefepime combination exerted synergism against most strains tested in broth microdilution assay. Time-kill profiles showed that both Leu-teixobactin and cefepime predominantly exhibited synergistic activity, with > 2.0-logCFU decrease compared to monotherapy at 24 h. Moreover, biofilm assays revealed a significant inhibition of biofilm production in ATCC™43300 cells treated with sub-MICs of Leu-teixobactin and cefepime. Subsequent electron microscopy studies showed more extensive damage with the combination therapy compared to monotherapies, including aberrant bacterial morphology, vesicle formation and substantial lysis, indicating combined damage to the cell wall. Quantitative real-time PCR revealed marked perturbation of genes mecA, sarA, atlA, and icaA, substantiating the apparent mode of combined antibacterial action of both antibiotics against peptidoglycan synthesis and initial biofilm production. Hence, the study highlights the prospective utility of the Leu-teixobactin-cefepime combination in treating MRSA infections via β-lactam potentiation.