Spermine increases bactericidal activity of silver-nanoparticles against clinical methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged worldwide as a major multidrug-resistant pathogen that causes notable morbidity and mortality. Fast emerging of MRSA prevalence requires special attention for strengthening the inventory of antimicrobial compounds. Silver nanoparticles (AgNPs) have been widely used to treat multi-drug resistant pathogens due to the unique antibacterial properties, meanwhile spermine has been proven to exert outstanding inhibition effect to S. aureus with not yet fully understood mechanisms. The aim of this study was to investigate the synergistic effect of AgNPs and spermine as well as to determine the antibacterial activity of their combination against MRSA strains. Several clinical MRSA isolates and ATCC BAA-1026 were used to determine minimum inhibitory concentration (MIC) and fractional inhibitory concentration indices (FICI) of AgNPs and spermine, and a synergistic effect was observed. This phenomenon was further confirmed by growth curve and time-killing assays, showed that spermine could be used as an adjuvant for AgNPs in the treatment of MRSA infections.