Synergistic antibacterial activity of the combination of the alkaloid sanguinarine with EDTA and the antibiotic streptomycin against multidrug resistant bacteria

Objectives: Drug combinations consisting of the DNA intercalating benzophenanthridine alkaloid sanguinarine, the chelator EDTA with the antibiotic streptomycin were tested against several Gram-positive and Gram-negative bacteria, including multi-resistant clinical isolates.

Methods: Microdilution, checkerboard and time kill curve methods were used to investigate the antibacterial activity of the individual drugs and the potential synergistic activity of combinations.

Key findings: Sanguinarine demonstrated a strong activity against Gram-positive and Gram-negative bacteria (minimum inhibitory concentrations, MIC = 0.5-128 μg/ml), while streptomycin was active against Gram-negative strains (MIC = 2-128 μg/ml). EDTA showed only bacteriostatic activity. Indifference to synergistic activity was seen in the two-drug combinations sanguinarine + EDTA and sanguinarine + streptomycin (fractional inhibitory concentration index = 0.1-1.5), while the three-drug combination of sanguinarine + EDTA + streptomycin showed synergistic activity against almost all the strains (except methicillin-resistant Staphylococcus aureus), as well as a strong reduction in the effective doses (dose reduction index = 2-16 times) of sanguinarine, EDTA and streptomycin. In time kill studies, a substantial synergistic interaction of the three-drug combination was detected against Escherichia coli and Klebsiella pneumoniae.

Conclusions: The combination of drugs, which interfere with different molecular targets, can be an important strategy to combat multidrug resistant bacteria.