Green Synthesis of Silver Nanoparticles using Spirulina maxima and their Antibacterial Activity against Staphylococcus spp.
Abstract
Antimicrobial resistance (AMR) among bacterial pathogens has emerged as a serious global concern, posing significant challenges to both human and animal health. The continuous rise in resistant strains has reduced the effectiveness of conventional antibiotics, necessitating the development of alternative and sustainable antimicrobial strategies. In this context, nanotechnology has gained considerable attention due to its potential applications in biomedical and veterinary sciences. The present study aimed to synthesize silver nanoparticles (AgNPs) using an aqueous extract of Spirulina maxima through an eco-friendly green synthesis approach and to evaluate their antibacterial efficacy. The biosynthesis of silver nanoparticles was indicated by a distinct colour change from pale yellow to dark brown due to the reduction of silver ions. The synthesized nanoparticles were characterized using dynamic light scattering (DLS) to determine particle size distribution and stability. The antibacterial activity of the synthesized AgNPs was assessed against Staphylococcus spp. using the agar well diffusion method at different concentrations (20, 40, 60, and 80 µL). The results revealed a clear concentration-dependent increase in antibacterial activity, with zones of inhibition measuring 8 mm, 10 mm, 12 mm, and 14 mm, respectively. The standard antibiotic ciprofloxacin exhibited a zone of inhibition of 16 mm, whereas the algal extract alone showed negligible activity. The findings of this study demonstrate that Spirulina maxima-mediated silver nanoparticles possess significant antibacterial potential and could serve as an eco-friendly and sustainable alternative to conventional antimicrobial agents. Further investigations are warranted to explore their mechanisms of action and practical applications in veterinary and biomedical fields.
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Introduction
Antimicrobial resistance (AMR) has emerged as one of the most critical global health challenges affecting both human and animal populations. The indiscriminate and excessive use of antibiotics has accelerated the development of resistant bacterial strains, leading to reduced drug efficacy, prolonged illness, and increased mortality (World Health Organization, 2014; Ventola, 2015). This alarming situation necessitates the exploration of alternative and sustainable antimicrobial strategies.
Conventional antibiotics act by targeting specific cellular structures or metabolic pathways of microorganisms. However, bacteria have evolved multiple resistance mechanisms, including enzymatic degradation of antibiotics, alteration of target sites, decreased permeability, and active efflux systems (Ventola, 2015). The rapid emergence of resistance, coupled with the slow discovery of new antibiotics, has intensified the need for innovative approaches to combat microbial infections.
Nanotechnology has recently gained significant attention as a promising field in biomedical and veterinary sciences. Among various nanomaterials, silver nanoparticles (AgNPs) have been extensively studied due to their broad-spectrum antimicrobial properties (Rai et al., 2009; Franci et al., 2015). These nanoparticles possess unique physicochemical characteristics such as high surface area-to-volume ratio, enhanced reactivity, and nanoscale size, enabling effective interaction with microbial cells.
Silver nanoparticles exhibit antimicrobial activity through multiple mechanisms, including disruption of cell membrane integrity, generation of reactive oxygen species, interaction with intracellular components, and inhibition of essential enzymes (Morones et al., 2005; Kim et al., 2007; Durán et al., 2016). These multiple modes of action reduce the likelihood of resistance development, making AgNPs a promising alternative to conventional antibiotics (Lara et al., 2011).
The synthesis method plays a crucial role in determining the biological activity and safety of nanoparticles. Conventional physical and chemical methods often involve toxic reagents, high energy requirements, and environmentally hazardous by-products (Iravani, 2011). In contrast, green synthesis using biological materials has emerged as an eco-friendly, cost-effective, and sustainable alternative (Ahmed et al., 2016; Singh et al., 2016).
Biological entities such as plants, algae, bacteria, and fungi contain a wide range of bioactive compounds that can act as reducing and stabilizing agents during nanoparticle synthesis. Among these, algae have gained particular attention due to their rich composition of proteins, polysaccharides, pigments, vitamins, and secondary metabolites (El-Rafie et al., 2014).
Spirulina maxima, a filamentous cyanobacterium, is widely recognized for its nutritional and medicinal properties. It contains various bioactive compounds that exhibit antioxidant, anti-inflammatory, immunomodulatory, and antimicrobial activities (Priyadarshini and Rath, 2012). The presence of diverse functional groups in Spirulina maxima makes it an ideal candidate for green synthesis of nanoparticles.
Several studies have demonstrated the successful synthesis of silver nanoparticles using biological systems and their antimicrobial efficacy (Ghosh et al., 2012). However, variations in biological sources and synthesis conditions can significantly influence nanoparticle properties and activity. Therefore, systematic studies focusing on specific biological materials are essential.
In this context, the present study was designed to synthesize silver nanoparticles using an aqueous extract of Spirulina maxima through a green synthesis approach and to evaluate their antibacterial activity. The study aims to highlight the potential of biologically synthesized nanoparticles as eco-friendly and effective alternatives to conventional antimicrobial agents.
Conclusion
The present study successfully demonstrated the green synthesis of silver nanoparticles using an aqueous extract of Spirulina maxima and confirmed their significant antibacterial activity against Staphylococcus spp. The biosynthesized nanoparticles exhibited a clear concentration-dependent antimicrobial effect, with zones of inhibition increasing from 8 mm to 14 mm as the concentration increased from 20 µL to 80 µL. DLS analysis confirmed the nanoscale size (Z-average: 78.4 nm) and acceptable stability (PDI: 0.28) of the synthesized nanoparticles.
The eco-friendly and cost-effective nature of the green synthesis approach, combined with the biological properties of Spirulina maxima, makes this method highly suitable for sustainable nanoparticle production. Although the antibacterial activity of the synthesized nanoparticles was slightly lower than that of the standard antibiotic ciprofloxacin, the results clearly highlight their promising role as an alternative antimicrobial strategy, especially in the context of increasing antimicrobial resistance.
Overall, Spirulina maxima-mediated silver nanoparticles can be considered a potential candidate for future applications in veterinary and biomedical fields. Further studies focusing on detailed characterization using advanced techniques (UV-Vis, TEM, FTIR), determination of minimum inhibitory concentration, mechanism of action, toxicity evaluation, and in vivo applications are recommended to validate their practical utility.
References
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