Combined efficacy of thymol and silver nanoparticles against Staphylococcus aureus

Due to the looming spread of resistance to classical antimicrobial agents, innovative therapeutic methods are in dire need to combat the onslaught of resistant bacterial pathogens. This study examines the antimicrobial efficacy of a phytochemical and a metallic nanoparticle against the top Gram positive resistant pathogen. The potential synergy of these two agents was also evaluated. The antibacterial activity of thymol and silver nanoparticles were tested individually using disc diffusion technique. The extent of synergy of their combination was evaluated using the checkerboard assay. Twenty clinical isolates of Staphylococcus aureus characterized as methicillin resistant or methicillin sensitive Staphylococcus aureus were utilized and the extent of synergism was calculated from fractional inhibitory concentration indices. Thymol exhibited an antistaphylococcal activity regardless of whether the isolates were phenotypically resistant or sensitive to methicillin. Combining thymol with silver nanoparticles resulted in at least additive or synergistic effect for all the examined strains and methicillin resistant strains were inhibited in the combinatorial assays to a greater extent comparative to when silver nanoparticles or thymol were used singly.     Key words: Silver nanoparticles, thymol, Staphylococcus aureus, synergy, fractional inhibitory concentration index.