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Biological synthesis of nanoparticles employing plants and their extracts is cheap and eco-friendly technique as compared to physical and chemical procedures that are expensive and hazardous to the environment. In this study, Zinc oxide (ZnO) nanoparticles were synthesized using leaf extract of Raphanus sativus. Energy Dispersive X-ray, Scanning Electron Microscopy and X-ray Diffraction were used for characterization. In-vitro, antibacterial activity against, Listeria monocytogenes, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus, and antifungal activity against, Candida albicans and Aspergillus flavus were investigated. Furthermore, the influence of precursor salt and capping agent concentrations on the size, morphology and subsequently on the antimicrobial activity of nanoparticles was examined by synthesizing six samples of ZnO nanoparticles at varying concentrations of zinc sulphate heptahydrate (ZnSO4·7H2O) and R. sativus leaf extract. Synthesized nanoparticles were spherical shaped and their size and agglomeration inclined with increasing zinc sulphate concentration, while declined with increasing R. sativus leaf extract. The antimicrobial results varied with the size and concentration of ZnO nanoparticles proving that these are two significant factors affecting their antimicrobial activity. The work reported in this paper demonstrates that R. sativus leaf extract can be successfully employed for the synthesis of ZnO nanoparticles for their antimicrobial applications.

The human serum is a vital component of the innate immunity of the host that acts as the first line of defence against invading pathogens. A key player in serum-mediated innate immune defence is a system of more than 35 proteins, collectively named as the complement system. After exposure of the pathogen, these proteins are activated in a cascade manner, ultimately forming a membrane attack complex (MAC) on the surface of the pathogen that directly lyses the bacterial cell. Formation of the MAC can be demonstrated in vitro by using serum bactericidal assay (SBA) that works in the absence of cellular components of blood after incubating the serum along with bacteria. Here, we describe the age-related differences in the bactericidal activity of human serum against Pseudomonas aeruginosa, an opportunistic human pathogen causing an array of hospital and community-acquired infections.We demonstrate that adult sera were highly effective in the in vitro killing of Pseudomonas aeruginosa as compared to children and the elderly (p < 0.0001). Sera from children were seriously compromised in the killing P. aeruginosa, whereas elderly sera showed a reduced level of killing. Data revealed a positive correlation between age and serum-killing with higher coefficient of determination values of 0.34, 0.27, and 0.58 and p values of < 0.0001, < 0.001, and < 0.0001, respectively, after 60, 90, and 120 minutes of incubation. Hence, our study highlights the age-related difference in the bactericidal activity of human sera. We conclude that sera of children are totally compromised, whereas elderly sera are only partially compromised, in the killing of P. aeruginosa.

Zinc oxide nanoparticles were synthesized from the leaf extract of Brassica oleracea L. Acephala group (collard green) followed by their characterization using Scanning Electron Microscope (SEM), and Energy Dispersive X-ray (EDX). The antibacterial properties of zinc nanoparticles were tested against Gram-negative bacteria, Pseudomonas aeruginosa (ATCC ® 9027™), Escherichia coli (ATCC ® 8739™), Klebsiella pneumoniae (ATCC® BAA-1705™) and Gram-positive bacteria, Staphylococcus aureus (ATCC ® 6538™) and Listeria monocytogenes (ATCC ® 13932™), at four different concentrations (50.00 µg/ml, 100.00 µg/ml, 500.00 µg/ml and 1 mg/ml) of zinc oxide nanoparticles suspension. Results revealed that the synthesized nanoparticles exhibit strong antibacterial effects against Pseudomonas aeruginosa, Listeria monocytogenes, Klebsiella pneumonia, Staphylococcus aureus and Escherichia coli at 500.00 µg/ml-1 mg/ml concentrations. An increase in efficacy of nanoparticles with the decrease of their size was also evident. This is a first ever report on Brassica oleracea, L. based nanoparticles which demonstrates that 500.00 µg-1 mg/ml conc. of zinc oxide nanoparticles have antibacterial activity against both Gram -ve and Gram +ve bacteria and have the potential to be considered as an antibacterial agent in future.

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