Abstract
Biogenic nanoparticles are the smartest weapons to deal with the multidrug-resistant “superbugs” because of their broad-spectrum antibacterial propensity as well as excellent biocompatibility. The aqueous biogenic silver nanoparticles (Aq-bAgNPs) and ethanolic biogenic silver nanoparticles (Et-bAgNPs) were synthesized using aqueous and ethanolic extracts of Andrographis paniculata stem, respectively, as reducing agents. Electron microscopic images confirmed the synthesis of almost spherical shaped biogenic silver nanoparticles (bAgNPs). The zeta potentials of the nanoparticles were negative and were −22 and −26 mV for Aq-bAgNPs and Et-bAgNPs, respectively. The antibacterial activity of bAgNPs was investigated against seven pathogenic (i.e., enteropathogenic Escherichia coli, Salmonella typhi, Staphylococcus aureus, Vibrio cholerae, Enterococcus faecalis, Hafnia alvei, Acinetobacter baumannii) and three nonpathogenic (i.e., E. coli DH5α, E. coli K12, and Bacillus subtilis) bacteria at different time points (i.e., 12, 16, 20, and 24 h) in a dose-dependent manner (i.e., 20, 40, and 60 μg) through broth dilution assay, disk diffusion assay, CellToxTM Green uptake assay, and trypan blue dye exclusion assay. The lowest minimum inhibitory concentration value for both the bAgNPs was 0.125 μg. Et-bAgNPs showed the highest antibacterial activity against S. aureus at 60 μg after 16 h and the diameter of inhibited zone was 28 mm. Lipid peroxidation assay using all the bacterial strains revealed the formation of malondialdehyde–thiobarbituric acid adduct due to the oxidation of cell membrane fatty acids by bAgNPs. The bAgNPs showed excellent hemocompatibility against human as well as rat red blood cells. Furthermore, there was no significant toxicity observed when the levels of rat serum ALT, AST, γ-GT (i.e., liver function biomarkers), and creatinine (i.e., kidney function biomarker) were determined.
Highlights
Pathogenic bacteria are the real threat to mankind due to their ability to develop resistance mechanism against the commercially available antibiotics (Aslam et al, 2018)
We have investigated the hemocompatibility of bAgNPs against human as well as rat red blood cells (RBCs)
The change of color confirms the reduction of Ag1+ to Ag0 due to the presence of secondary metabolites including flavonoids and different types of andrographolides in A. paniculata stem extract (Singh et al, 2018)
Summary
Pathogenic bacteria are the real threat to mankind due to their ability to develop resistance mechanism against the commercially available antibiotics (Aslam et al, 2018). Silver nanoparticles (AgNPs) have been widely used in pharmaceuticals and cosmetics and in the treatment of water because of their antibacterial propensity against a wide range of bacteria (Ramalingam et al, 2016). Silver nanoparticles are not toxic for the human healthy peripheral lymphocytes (Gengan et al, 2013) They have high affinity and significant toxicity to bacteria as well as cancer cells (Greulich et al, 2012; Gengan et al, 2013). The antibacterial potential of bAgNPs was investigated against seven pathogenic bacterial strains including enteropathogenic E. coli (EPEC), Salmonella typhi, S. aureus, Vibrio cholerae, Enterococcus faecalis, Hafnia alvei, and Acinetobacter baumannii. The effect of bAgNPs on liver and kidneys was investigated through determining the level of serum ALT, AST, and γ-GT as liver function biomarkers and serum creatinine as kidney function biomarker
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