The antibacterial potential of biosynthesized silver nanoparticles using beech bark and spruce bark extracts

Abstract Introduction: Lately, nanotechnology focuses on the green synthesis of AgNPs, using different plant materials, as this method is accessible, cost-efficient, and ecological. The study aimed to investigate the antibacterial potential of AgNPs synthesized using beech/spruce bark extracts (BBE/SBE) and silver salts (acetate/nitrate). Method: The growth rates of Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922 were evaluated in the presence of the AgNPs solutions. The checkerboard method was performed to evaluate if these solutions exert synergistic activity with gentamicin. Results: For E. coli, synergistic effects were observed for the combination of gentamicin 0.25mg/L with AgNP BBE Nit (0.145mg/mL) and with AgNP SBE Ac (0,09mg/mL). For S. aureus, no synergistic effects were observed. Overall, the AgNP BBEs solutions combined with gentamicin presented lowest values of fractional inhibitory concentration than the ones registered for the combination of AgNP SBEs with gentamicin, for both bacterial strains. The growth rate of S. aureus was inhibited by all the tested AgNPs at the measured time points. For E. coli, after 24 hours of incubation, the growth rate was inhibited only in the presence of AgNP SBE Ac. After 6 hours of incubation, the growth rate of E. coli was almost stationary in the presence of AgNP BBE Nit. Conclusions: The biosynthesis of AgNPs is a valuable choice for obtaining substances with antibacterial potential.