aureus and Gram-negative bacteria such as, P. Several studies have reported antibacterial activity of copper oxide NPs against Gram-positive bacteria, such as B. Recently, metallic copper, cupric oxide (CuO) and cuprous oxide (Cu 2O) nanoparticles are gaining mounting attention due to their widespread application in electronic, optical sensors, catalysts and therapeutic applications 14, 15, 16. Diverse simultaneous mechanisms of action of nanoparticles against bacteria would make it hardly possible for the microbes to develop resistance, as the bacterial cell would be required to make multiple simultaneous gene mutations to develop this resistance 2. Nanoparticles provide a way to address “common antibiotic resistance mechanisms such as regulation of permeability, multi-drug efflux pumps, antibiotic degradation and target site binding affinity mutations” 13. A variety of antibiotic resistant infectious diseases have been treated both in vitro and in vivo animal models by numerous classes of nanoparticles and nanoscale antibiotic carriers 1. Intrinsic tendency of boosted release of metallic ions and close interaction of nanoparticles with bacterial membranes which are accountable for antibacterial activity of nanoparticles can be attributed to their high surface area to volume ratio 9. Nanoparticles exhibit fascinating mechanical, magnetic, electrical and optical properties as well as high adsorption and catalytic competencies compared to their bulk counterparts owing to their nanodimensions (1–100 nm range) 1, 10, 11, 12. In recent efforts to address this challenge, metallic and metallic oxide nanoparticles have emerged as significant and novel antimicrobial agents 5, 6, 7, 8, 9. Appallingly, there is no guarantee that new antimicrobial drugs can cope with the rapid and frequent development of resistance of the microbial pathogen in a timely manner 5. Discovery of new antibiotics and chemical modification of the existing antimicrobial drugs are among the exceedingly sought-after strategies to address the challenge of bacterial resistance to antibacterial drugs. The calamity of antibiotic resistance has been attributed to the overuse and misuse of these drugs, along with the pharmaceutical industry's lack of new drug development due to reduced economic incentives and challenging regulatory requirements 4. The increasing frequency of antibiotic resistance in many bacterial pathogens with subsequent failure of antibiotic therapy, especially in intensive care unit patients, has led to hundreds of thousands of deaths annually 3. The genesis and an alarming spread of “multi-drug-resistant (MDR) bacteria” has become a severe peril to public health all over the world compromising the effectiveness of antibiotics 1, 2. The results suggest that lipopeptide biosurfactant stabilized Cu 2O NPs could have promising potential for biocompatible bactericidal and therapeutic applications. Flow cytometric quantification of intracellular reactive oxygen species (ROS) using 2,7-dichlorodihydrofluorescein diacetate staining revealed a significant ROS generation up to 2.6 to 3.2-fold increase in the cells treated with 62.5 µg/mL Cu 2O NPs compared to the untreated controls, demonstrating robust antibacterial activity. MTT cell viability assay displayed a median inhibition concentration (IC 50) of 21.21 μg/L and 18.65 μg/mL for P. The lipopeptide stabilized Cu 2O NPs with an ultra-small size of 30 ± 2 nm diameter exhibited potent antimicrobial activity against both Gram-positive and Gram-negative bacteria with a minimum inhibitory concentration of 62.5 µg/mL at pH5. aeruginosa CB1 strains, based on cell viability, zone of inhibition and minimal inhibitory concentration (MIC) indices. The antibacterial activity of the as-synthesized Cu 2O NPs was evaluated against Gram-positive B. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive x-ray spectrum (EDX) and UV–Vis analysis were carried out to investigate the morphology, size, composition and stability of the nanoparticles synthesized. Cuprous oxide nanoparticles (Cu 2O NPs) were fabricated in reverse micellar templates by using lipopeptidal biosurfactant as a stabilizing agent.
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