RESUMO
Background and Aim: Antibiotic resistance, especially in Gram-negative bacteria, is a major public health risk affecting all industries requiring the use of antibiotics, including agriculture and animal breeding. This study aimed to use papaya extracts to synthesize silver nanoparticles (AgNPs) and evaluate their antimicrobial activity against various Gram-negative bacteria. Materials and Methods: Silver nanoparticles were synthesized from the aqueous extracts of papaya seed, root, and bark, with AgNO3 used as a reducing agent. The phytofabricated AgNPs were analyzed by ultraviolet-visible absorbance, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy, and photon cross-correlation spectroscopy (PCCS). The disc-diffusion method was used to perform antibacterial analysis, and the minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations were determined. We also investigated the antibiofilm activity of AgNPs and attempted to elucidate the potential mechanism of action on Escherichia coli ATCC 25922. Results: Phytofabrication of AgNPs was successful with papaya root (PR-AgNPs) and papaya seed (PS-AgNPs), but not with papaya bark. Silver nanoparticles using papaya root and PS-AgNPs were both cubic and showed maximum absorbances of 2.6 and 0.3 AUs at 411.6 and 416.8 nm wavelengths and average hydrodynamic diameters X50 of 59.46 ± 7.03 and 66.57 ± 8.89 nm, respectively. The Ag in both AgNPs was confirmed by X-ray fluorescence by a distinctive peak in the spectrum at the silver Kα line of 22.105 keV. Both AgNPs exhibited broad-spectrum antimicrobial and antibiofilm activity against all Gram-negative bacteria, and PR-AgNPs were slightly better than AgNPs-PS. The MIC ranged from 16 µg/mL-128 µg/mL and 16 µg/mL-64 µg/mL, respectively, for PS-AgNPs and PR-AgNPs. The elucidation of the mechanism of action revealed interference with E. coli ATCC 25922 growth kinetics and inhibition of H+-ATPase proton pumps. Conclusion: Papaya seed and root extracts were efficient reducing agents for the biogenic synthesis of AgNPs, with noteworthy antibacterial and antibiofilm activities. Future studies should be conducted to identify the phytochemicals and the mechanism involved in AgNPs synthesis.
RESUMO
Background and Aim: Resistance to antifungal agents is a serious public health concern that has not been investigated enough because most studies on antimicrobials are dedicated to antibacterial resistance. This study aimed to synthesize silver nanoparticles (AgNPs) using Aloe vera extract, and to assess its antifungal activity against Candida albicans. Materials and Methods: Silver nanoparticles were synthesized by reducing Ag nitrate with aqueous A. vera extracts. Physicochemical properties of synthesized AgNPs were determined by ultraviolet-visible spectrophotometry, photon cross-correlation spectroscopy, energy-dispersive X-ray fluorescence spectrometry, X-ray diffraction analysis, and Fourier-transform infrared spectroscopy. An antifungal investigation was performed against four clinical C. albicans (C1, C2, C3, and C4) and a reference strain, C. albicans ATCC 10321. Results: Cubic AgNPs with a mean X50 hydrodynamic diameter of 80.31 ± 10.03 nm were successfully synthesized. These AgNPs exhibited maximum absorbance at 429.83 nm, and X-ray fluorescence (XRF) confirmed the presence of Ag in AgNPs solution by a characteristic peak in the spectrum at the Ag Kα line of 22.105 keV. Infrared spectra for AgNPs and A. vera extract indicated that the compounds present in the extract play an essential role in the coating/capping of synthesized AgNPs. Different concentrations (200, 100, 50, 25, 10, and 5 µg/mL) of AgNPs were tested. The antifungal activity was shown to be dose-dependent with inhibition zones ranging from 10 mm to 22 mm against C. albicans ATCC 10231, 0 mm to 15 mm against C1, 0 mm to 16 mm against C2 and C3, and 0 mm to 14 mm for C4. Minimum inhibitory concentration ranged from 16 µg/mL to 32 µg/mL against clinical C. albicans (C1, C2, C3, and C4) and was 4 µg/mL against C. albicans ATCC 10231. Conclusion: This study showed the ability of A. vera to serve as an efficient reducing agent for the biogenic synthesis of AgNPs with excellent antifungal activity.
