Synthesis of Biogenic Silver Nanoparticles Using Caesalpinia digyna and Investigation of Their Antimicrobial Activity and In Vivo Biocompatibility

Abstract

Among metallic nanoparticles, silver nanoparticles (AgNPs) have a wide spectrum of medical applications. Herein, biogenic silver nanoparticles (bAgNPs) were prepared from extracts of Caesalpinia digyna leaf as a reducing agent at different pH values (i.e., 5, 7, 8, and 10). The as-synthesized bAgNPs were characterized using UV–vis and Fourier transform infrared (FTIR) spectroscopies, scanning transmission electron microscopy, powder X-ray diffraction analysis, dynamic light scattering, and ζ-potential analysis. The sizes of bAgNPs prepared at pH 5, 7, 8, and 10 were 45.4, 11.3, 11.4, and 40.8 nm, respectively, and all of the nanoparticles were negatively charged. The antimicrobial activity of the as-prepared bAgNPs was investigated against Bacillus subtilis, Escherichia coli DH5α, E. coli K12, enteropathogenic E. coli (EPEC), and Salmonella typhi. The bAgNPs prepared at pH 8 showed the highest antibacterial propensity against all of the bacterial strains as exhibited in the zone of inhibition (ZOI) as well as the CellTox green assay, which can be due to their relatively small size, stability, and higher surface area-to-volume ratio. The bAgNPs synthesized at pH 8 showed the highest ZOI against B. subtilis, which was ∼25 mm in diameter. The lipid peroxidation assay demonstrated the formation of the malondialdehyde-thiobarbituric acid (MDA-TBA) adduct while treating the bacteria with bAgNPs due to the oxidation of fatty acids present in the membrane. The highest amount of MDA-TBA adduct was observed when Gram-positive B. subtilis was exposed to bAgNPs. On the contrary, rats treated with bAgNPs demonstrated no significant toxicity in terms of hematological and biochemical parameters. The bAgNPs also showed excellent compatibility with human red blood cells. Overall, bAgNPs synthesized at pH 8 have superior antimicrobial activity and excellent biocompatibility and, therefore, can be used as potential antibacterial agents.

Investigation of the Antimicrobial Activity and <i>in Vivo </i> Cytotoxicity of <i>Diospyros malabarica </i> (Desr.) Kostel. Fruit Extracts

“…The antimicrobial activity of D. malabarica seed and flesh extracts was determined by disk diffusion method as described previously [23,24]. Briefly, bacterial strains (i.e., E. coli DH5α, B. subtilis RBW, and S. typhi) were cultured in LB medium at 37˚C and 120 rpm overnight.…”

“…Trypan blue dye exclusion assay was performed for the bacteria treated with D. malabarica seed and flesh extracts according to our previously published protocol with little modifications [23][24][25]. Briefly, 4 mg of plant extracts was mixed separately with 50 μl of diluted overnight grown culture (OD: 1.3 -1.4) of the respective bacterial strains (i.e., E. coli DH5α, B. subtilis RBW, and S. typhi) and incubated at 37˚C and 120 rpm for 2 hours.…”

“…The lipid peroxidation (LPO) potential of D. malabarica seed and flesh extracts was investigated according to our previously published protocol [23][24][25]. Briefly, 200 µl of the overnight grown bacterial cultures (OD: 1.4 -1.6) was mixed separately with 4 mg of each of the plant extracts.…”

“…LPO assay was performed to determine the oxidation ability of D. malabarica seed and flesh extracts to bacterial cell membrane fatty acids [23,25]. As the oxidation of fatty acids brings about the disruption of cell membrane integrity, it can be an effective way to kill the bacteria [23,24]. Hence, the cell membrane fatty acid oxidation potential of the D. malabarica extracts was investigated through measuring the absorbance of malondialdehyde-thiobarbituric acid (MDA-TBA) pink adduct at 532 nm (Figure 7).…”

Investigation of Antimicrobial Activity and Biocompatibility of Biogenic Silver Nanoparticles Synthesized using Syzigyum cymosum Extract

“…Rats treated with bAgNPs demonstrated no significant toxicity in terms of hematological and biochemical parameters. 14 , 15 …”