Synergistic antimicrobial activity of bacteriophages and antibiotics against Staphylococcus aureus.

This study was designed to assess the synergistic antimicrobial effect of phages combined with antibiotics against Staphylococcus aureus. The phage-antibiotic synergy (PAS) effect was evaluated using the fractional inhibitory concentration (FIC) and flow cytometric analysis. The determined minimum inhibitory concentration (MIC) values varied from 0.125 to 128 μg/mL for S. aureus KACC 13236 (SAS) and from 0.25 to >256 μg/mL for S. aureus CCARM 3080 (SAR). The PAS effect was more pronounced in SAS treated with phage SA11 in the presence of cefoxitin (FIC=0.62), chloramphenicol (FIC=0.54), and polymyxin B (FIC=0.38). SAS and SAR cells were injured when exposed to asublethal concentration of ciprofloxacin, whereas these cells were highly susceptible to the phage-antibiotic combined treatment, showing 96% of relative percentages of injured and dead cells. The results suggest that the combined treatment of phages and antibiotics can be used to improve antimicrobial efficacy against antibiotic-resistant bacteria.