Green synthesis of silver nanoparticles facilitated by cyanobacterium Lyngbya confervoides with their metabolite profiling, characterisations and antibacterial evaluations

This study aimed to culture the cyanobacterium Lyngbya confervoides (Lc) biomass for the preparation of crude aqueous and methanol extracts, and for a preliminary phycochemical investigation and molecular docking study. Biosynthesis of Lc-silver nanoparticles (Lc-AgNPs) was carried out, and nanoparticles were characterised using spectroscopic and microscopic techniques, followed by assessment of in vitro antibacterial efficacy against four multidrug-resistant (MDR) pathogens. FESEM confirmed the moderate nanoscale morphology (∼100 nm) of the Lc-AgNPs; XRD confirmed their crystalline nature; FTIR showed functional groups; and DLS observed a polydisperse size distribution. The antibacterial activity of Lc-AgNPs was evaluated against Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli and Acinetobacter baumannii with inhibition zones of 12–16 mm and MIC concentrations of 25–50 μg/mL. MTT assay with THP-1 showed higher toxicity, with 50% reduction in cell number and an IC50 of about 20 μg/mL, compared to crude Lc (75 μg/mL) after 48 hours. Overall, the findings demonstrated the potential of Lc-AgNPs as an antibacterial agent and revealed the need for further pharmacological studies to optimise therapeutic doses.