Investigating the effect of biosynthesized silver nanoparticles as antibiofilm on bacterial clinical isolates

Silver nanoparticles showed enhanced biofilm inhibitory activity of clinical pathogens. Eleven isolates (45.8%) of E. coli bacteria were obtained from 24 wound specimens. Silver nanoparticles biosynthesized by E. coli culture supernatant with exhibition dark brown color after 24 hr of incubation. Scanning electron microscopy showed that Ag-NPs spherical particles and its size were (14.2-67.8) nm and its average was 33.6 nm. X-ray diffraction shows one high peak at 2ø (32.5°) compared with standard data. Fourier transform infrared spectroscopy analysis of Ag-NPs exposed the strong band at 1367.53 corresponds to OH-bend which influences the synthesis and stability of Ag-NPs, whereas the stretch for Ag-NPs found at 518.58 cm^-1. The antibacterial effect of Ag-Nps against E. coli, P. aeruginosa, K. pneumoniae and S. aureus showed the inhibition zone of 10, 11, 13, and 10 mm, respectively. Strong biofilm formed by isolates of E. coli exhibited as black colonies on Congo red agar, while pink colonies on it with Ag-Nps, indicating a loss of biofilm formation ability in all tested bacterial isolates. Antibiofilm of 10 mM Ag-Nps by Microtiter plate exhibited lower biofilm inhibition against S. aureus reached to 22.2%, while 36.2% against E. coli, 30.4% for K. pneumonae, and P. aeruginosa 94.7%. Analysis of biofilm components after exposure to Ag-NPs by FT-IR reveals a low level of proteins, polysaccharides, lipids and nucleic acids compared with controls, then glucose formation measured and exhibited reduction of absorbance (0.146 nm) after treatment with Ag-Nps compared with control (0.347 nm), while the percentage of protein decreased completely (0%) compared with control (0.25%). The combined effect of Ag-NPs with antibiotics enhanced the antibiofilm activity which tested under inverted microscope (40X).