Zinc oxide nanoparticles (ZnO NPs) have been widely used in biomedical applications due to their high biocompatibility and low toxicity to humans. The present work aimed to investigate the antibacterial effects of different concentrations of ZnO NPs on two opportunistic pathogens, Serratia marcescens and Enterococcus faecalis. The surface interaction between nanoparticles and bacterial cell wall, and the subsequent morphological alterations on the bacterial surface, were examined through Fourier transform infrared spectroscopy and scanning electron microscope. The energy dispersive X-ray analysis was used to confirm the elemental composition of ZnO NPs and the cellular accumulation of ZnO NPs in bacteria. The growth-inhibitory test demonstrated a dose-dependent growth inhibitory effect of ZnO NPs against both the test bacteria, as the higher concentration of nanoparticles caused the higher bacterial growth inhibition. The results showed that ZnO NPs caused a higher growth inhibition (63.50 ± 2.50%) on the Gram-positive bacterium E. faecalis compared to the Gram-negative bacterium S. marcescens (51.27 ± 4.56%). Fourier transform infrared spectrum revealed the possible involvement of hydroxyl, carboxyl, amides, methylene, and phosphate groups from the biomolecules of bacterial cell wall such as proteins, carbohydrates, lipids, and phospholipids in the interaction of ZnO NPs on bacterial cell surface. Energy dispersive X-ray analysis showed the higher accumulation of ZnO NPs in E. faecalis than S. marcescens analogous to the bacterial growth inhibition. Scanning electron microscopy images confirmed the antibacterial properties of ZnO NPs, showing the loss of integrity of cell membrane and distortion of bacterial cells. Hence, the potential of ZnO NP as an antibacterial agent against S. marcescens and E. faecalis has been confirmed.
Viruses can spread worldwide and the early detection of emerging infectious diseases and outbreaks in humans and animals is important for effective surveillance and prevention. Viruses such as human immunodeficiency virus (HIV), swine flu, and influenza virus are some of the viruses that spread diseases worldwide. However, the non-availability of effective antiviral drugs and the drug-resistance among the virus and host have become the major problems in controlling viral infections. The natural products from microalgae can be an alternative therapeutic agent to control viral infections in humans. Spirulina is a well-known cyanobacterium that has been consumed by humans as a food supplement for more than centuries without side-effects. Spirulina possesses high nutritional values and provides numerous health benefits to the consumers. Spirulina can be an alternative natural therapeutic agent for numerous virus infections as it contains several bioactive compounds with proven antiviral effect on enveloped viruses (Herpes simplex virus, measles virus, mumps virus) and non-enveloped viruses (astrovirus, rotavirus) by preventing the spread of the virus in the host cells. Spirulina also serves as a natural supplement that strengthens the immune system. This review focuses on the antiviral properties and immunostimulant effects of Spirulina as a potential therapeutic supplement on human health.
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