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Green synthesis of silver nanoparticles and their activity against bacterial biofilms

Emergence of new resistant strains of microorganisms to current antibiotics has become a major issue in public health; therefore, it is imperative to develop new bactericides. This study, thus, aimed at synthesizing silver nanoparticle (AgNPs) and determining their antibacterial activities on bacterial biofilms. Sachet water and well water samples were collected from sachet water industries and two hand-dung wells around Gbonagun piggery house, respectively from where isolation and identification of microorganisms was carried out using standard techniques. Identified bacterial isolates were screened for biofilm formation using tube test as well as Congo red method and the fungal isolate was used to synthesize AgNPs. The formation of silver nanoparticles was confirmed by the physical change of colour and absorption peak between 250-800 nm was evaluated using UV-Vis spectroscopy. Further, the synthesized AgNPs were characterized by Fourier transform infrared spectroscopy. Antibacterial activities of the silver nanoparticles on the biofilms formers was investigated using agar well diffusion method and the potential to prevent the growth of biofilms was evaluated. Predominant bacterium and fungi were Bacillus subtilis and Aspergillus species. Biofilm formers as revealed by the tube test and C ongo red method are: B. subtilis , Enterobacter cloacae, Proteus mirabilis, Klebsiella pneumoniae, Streptococcus pyogenes and Staphylococcus aureus. The color of the synthesized silver nanoparticles by A. niger was yellowish brown and control showed no colour change. The UV-visible spectra of the nanoparticles exhibited an absorbance peak at approximately 425 nm. The FTIR analysis revealed the presence of coordinating NH 2 , OH, amides I and II among others, ligating functional groups in the biomass of A. niger responsible for efficient capping and stabilizing of the AgNPs. Synthesized AgNPs prevented the growth of biofilm formers by exhibiting highest zone of inhibition of 18.5 mm. The ability of the synthesized silver nanoparticles to inhibit growth of bacterial biofilms by Bacillus subtilis presents the mould ( A. niger ) as a vital bioresource in synthetizing AgNPs with good bactericidal activities.