Extraction and Characterization of Silver Nitrate Modified Biopolymer and its Antimicrobial Mode of Action

Biopolymer (chitosan) was isolated from crab shell waste through the processes of demineralization, deproteinization, decolourization and deacetylation. The resulting chitosan (CHS) was further treated with silver nitrate (AgNO3) solution at various concentrations (0.5, 1.0 and 1.5 M) in order to enhance the antimicrobial activity of chitosan. The crab shell powder (CSP) and (CHS) were characterized using X-ray Diffractometer (XRD), Fourier Transform Infrared (FT-IR), and Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM-EDS). The antimicrobial mode of action of AgNO3 treated chitosan was performed using serial dilution (1:2) technique for minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) and tested against four microorganisms (Escherichia coli, Klebsiella pneumonia, Staphlococcusaureus and Pseudopodium). The result of proximate analysis of CHS and chitin (CHN) showed % crude protein to be 12.24±001 and 20.54±0.03 respectively, % ash was found to be 4.1±0.01 for CHS and 3.80±0.01 for CHN. The FTIR spectra of CHS and CHN showed their characteristic absorption peaks and the diffractograms of CSP and CHS showed CaCO3 to be the major mineral present in the samples. The antimicrobial evaluation revealed that untreated chitosan extract (UCHSE) showed no antimicrobial activity against the four tested microorganisms. The results of MIC and MBC showed that the organisms responded to the antimicrobial agent at different dilution concentration. It was observed that CHS treated with 0.5 M AgNO3 (0.5 SNCHSE) inhibited the growth of E. coli at 1000 µg/mL, S. aureus at 500 µg/mL while it exhibited bactericidal (MBC) activity against all the organisms at 1000 µg/mL.