Monitoring of antibacterial capabilities of biosynthesized gold nanoparticles facilitated cyanobacterium, Spirulina subsalsa, against MDR pathogenic bacteria.

Gold nanoparticles (AuNPs) were biosynthesized with the non-nitrogen fixing cyanobacterium Spirulina subsalsa (Ss-AuNPs), and their antibacterial properties were monitored. Several analytical techniques, i.e., UV-visible spectroscopy, dynamic light scattering, zeta potential, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy, were employed for characterization. Thereafter, antibacterial efficacies of the biosynthesized AuNPs against multidrug-resistant bacterial strains, Escherichia coli, Acinetobacter baumannii, Staphylococcus aureus, and Streptococcus pyogenes were assessed. During synthesis of nanoparticles, a color change signified a change in the oxidation state of gold, whereby electrons in nanoparticles respond to light, which creates the color change called "plasmon resonance." Bioactive substances such as proteins and polysaccharides, and pigments like phycocyanin are crucial in converting Au (III) ions to Au (0). Here, S. subsalsa underplays to reduce AuNPs. A color shifts from pale green to pink-purple by UV-visible spectra with a strong absorption peak at 531 nm. The zeta potential of - 50 mV could increase the capacity of the compounds to interact with bacterial membranes, therefore enhancing their antibacterial effect. The FTIR spectral examination yielded a range of absorbance bands at 3321, 1633, and 513 cm, which were bound to the surface of AuNPs for agglomeration prevention to provide colloidal stability that acts as a stabilizing agent. It could be taken as a novelty that Ss-AuNPs had potent antibacterial activities against four MDR pathogenic bacteria with cited zone of inhibition, E. coli (25 ± 0.5), A. baumannii (22 ± 0.5), S. aureus (25 ± 0.5), and S. pyogenes (27 ± 0.5) mm.