Citrus maxima extract-coated versatile gold nanoparticles display ROS-mediated inhibition of MDR-Pseudomonas aeruginosa and cancer cells.

The expanding prevalence of microbial resistance to conventional treatments has triggered a race to develop alternative/improved strategies to combat drug-resistant microorganisms in an efficient manner. Here, the lethal impact of the biosynthesized gold nanoparticles (AuNPs) against multi-drug resistant (MDR) bacteria has been elucidated. AuNPs, synthesized from the extracts of the fruit, leaf and peel of the Citrus maxima plant, were physicochemically characterized by UV-Vis spectrophotometry, Dynamic Light Scattering (DLS), electron microscopy and spectroscopic techniques not only confirmed the production of AuNPs of size below 100 nm but also identified the phytochemicals adsorbed onto the surface of NPs. AuFeNP not only showed excellent antioxidant activity (∼95 % at 1 mg/mL) but also exhibited a commendable antimicrobial activity against MDR-Pseudomonas aeruginosa as assessed by the zone of inhibition (13.5 mm) and microwell broth dilution assays (9.5 μg/mL, MIC). Transmission electron microscopy (TEM) displayed bacterial cell membrane destruction post-AuNPs exposure. The killing mechanism of AuNPs elucidated the permeabilization of the cell membrane and generation of reactive oxygen species (ROS), ∼10-fold high depletion of GSH, and eventually leaching protein out of the cell. DNA damage, as a marker of apoptosis, was also noticed, which could be an implication of ROS accumulation in MDR-PA. AuNPs displayed significant toxicity at ∼ 10 μg/mL on various cancer cells (HT-1080, MRC-5, MDA-MB-231 and B16-F10) and relatively low toxicity on normal cells (MRC-5 and HaCaT). Scratch assay to identify the migration capability of breast cancer cells on treatment with AuNPs deciphered hampering of migration potential of breast cancer cells. Apoptotic topographies in B16-F10 cells were confirmed using AO/EtBr dual dye staining, DNA fragmentation, Caspase-3 assay and cell cycle analysis using flow cytometry. Hemolysis revealed minimal toxicity of AuNPs on human red blood cells. Nominal toxicity (∼70 % survival at 500 μg/mL of AuNPs) on mammalian cells was evaluated using Cell Titer-Glo cell viability assay. Overall results advocate the promising potential of biosynthetic AuFeNP against multi-drug-resistant pathogens and for further formulation into anticancer agents.