Green synthesis of AgNPs from aqueous extract of Oxalis corniculata and its antibiofilm and antimicrobial activity

The silver nanoparticles OC-AgNPs, synthesized from the aqueous extract of Oxalis corniculata (OC), showed antiviral activity against Herpes Simplex Virus-1 (HSV-1), and anti-biofilm, and antibacterial activities against human isolates of six multi-drug resistant (MDR) bacteria - Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli, Klebsiella pneumoniae, Salmonella typhi, and Pseudomonas aeruginosa. The OC-AgNP was characterized by UV-Vis and FTIR spectroscopy; while its morphology and distribution were determined by transmission electron microscopy (TEM). The results revealed that the biogenic OC-AgNPs are spherical with an average diameter of 40 nm and has shown UV-Vis peak at 445 nm. The cytotoxicity and safety of OC-AgNP has been evaluated by MTT assay in Vero cells and triple-negative human breast cancer MDA-MB-468 cells. The plaque reduction assay has been used to test the antiviral activity against HSV-1F. The anti-biofilm activity was assessed by crystal violet staining, followed by light and confocal microscopy; while the antibacterial activity was determined by conventional disk-diffusion and broth-dilution methods. Moreover, the mechanism of anti-biofilm and antibacterial activity was examined by Field Emission Scanning Electron Microscopy (FESEM). The CC₅₀ (cytotoxicity) on Vero cells was 300 μg/ml; while the survival percentage of MDA-MB-468 cells was 27.12% at 20 μM and 80.97% at 100 μM of, respectively. The OC-AgNP showed moderate antiviral activity against HSV-1F at EC₅₀ of 25 μg/ml; but significantly inhibited the biofilm produced by Pseudomonus aeruginosa and Escherichia coli at 25-50 μg/ml; while at 30-50 μM we observed the dose-dependent lowering of fluorescence intensity under light and confocal microscope. Interestingly, the OC-AgNPs demonstrated significant antibacterial activity against Pseudomonas aeruginosa (20 mm), Klebsiella pneumoniae (15 mm), Escherichia coli (12 mm), Salmonella typhi (10 mm), Streptococcus pyogenes (11 mm) and Staphylococcus aureus (10 mm) with Minimum Inhibitory Concentration (MIC) of 0.65–0.90 μM (0.11- 0.153 μg), respectively. Further, the FESEM micrograph showed disruption of membrane structure with the damage of cell membrane integrity of Pseudomonus aeruginosa at its MIC.