Biosynthesis and characterisations of silver nanoparticles with filamentous cyanobacterium Lyngbya sp. with in vitro antibacterial properties against MDR pathogenic bacteria

This study describes phycocompounds of the non-N₂-fixing filamentous cyanobacterium Lyngbya sp., which has potential bio-reducing and stabilizing heavy metal-accumulating properties for synthesizing silver nanoparticles (AgNPs), whose formation was confirmed by the colour change of the Lyngbya sp.-AgNP solution from pale green to deep brown. The reduction of 'Lyngbya sp.-AgNPs', called Lsp-AgNPs, was proved by UV-visible photo-spectrometry analysis with an obtained peak value at 426 nm. Lsp-AgNPs were characterised by analytical techniques, XRD, FESEM, DLS and FTIR. The XRD analysis with 5-70 theta was obtained at 2ϴ angles ranging from 38.79º with intensity, indicating the crystal structure of Lsp-AgNPs. The FESEM analysis indicated the area size at 20-50 µm; in the DLS analysis, the peak at 400 d nm indicated the size and distribution of Lsp-AgNPs. In FTIR analysis, the peaks were obtained at wavenumbers 3338, 1639, and 542 cm^-1, which indicated the presence of N-H, -OH and C=O functional groups in Lsp-AgNPs. Those had in vitro antibacterial activities against Gram-negative Escherichia coli (MTCC 443) and Pseudomonas aeruginosa (MTCC 1688) and Gram-positive Staphylococcus aureus (MTCC 7443) bacterial strains with zone of inhibitions (ZOI) of 16, 12 and 14 mm, respectively, with comparing the antibiotic gentamycin as a positive control, as was monitored with agar-well diffusion method. Furthermore, the MIC value was 50 mg/ml, and MBC values of 65 mg/ml of Lsp-AgNPs were effective against those bacteria. Thus, Lsp-AgNPs had potential antibacterial activities against MDR pathogenic S. aureus, E. coli and P. aeruginosa. In conclusion, MDR pathogenic bacteria could be controlled as prodrugs in the future.