Domestic Wastewater Treatment: The Influence of Silver Impregnated Polyrhodanine Nanofibers on Gram-Positive and Gram-Negative Bacteria

Abstract

Abstract-Polyrhodanine nanofibers impregnated with silver nanoparticles were produced by a simultaneous chemical oxidation polymerization process in which the silver ions were reduced to silver nanoparticles onto the rhodanine monomer, which were then oxidized to construct the silver impregnated polyrhodanine nanofibers. The antimicrobial efficacy was tested by the disc diffusion method, broth dilution assay, as well as flow cytometry analysis to acquire significant information on the mechanisms of the nanoparticles and polymer complex. This complex resulted in excellent antimicrobial properties and inhibitory effects against both Gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli, Salmonella typhi). Disc diffusion analyses proved that the polyrhodanine-silver complex had superior antibacterial efficacy compared to the pristine silver nanoparticles. Gram-positive bacteria were found to be the most susceptible to the PRD-Ag complex with minimum inhibitory concentrations (MIC) of 12.5 µg/disc. The MIC of Gram-positive bacteria was slightly higher at 25 µg/disc. The investigation of the contact time of the nanomaterial with the various bacteria also supported the notion that a reduction in cell viability is more prominent in the presence of the synthesized PRD-Ag nanofibers compared to pristine silver nanoparticles. This study also demonstrated that the determination of total cell concentration by means of flow cytometry analysis is a rapid and sensitive method that could be widely applied in wastewater treatment technology. The flow cytometry analysis supported the initial findings and confirmed that the Gram-positive bacterial strains are more susceptible to the antibacterial complex with cell viability decreased to 51.10% for B. subtilis and a significant decrease to 5.33% for S. aureus.