Identifying molecular targets of a colloidal nanosilver formulation (Silversol®) in multidrug resistantPseudomonas aeruginosa

P. aeruginosa is a notorious pathogen. A multi-drug resistant strain of this bacterium was challenged with a colloidal nano-silver formulation- Silversol ® . Its minimum inhibitory concentration against P. aeruginosa was found to be 1.5 ppm, and at sub-MIC of 1 ppm, it was able to alter quorum-sensing regulated pigmentation, exopolysaccharide synthesis and biofilm formation, antibiotic susceptibility, protein synthesis and export, nitrogen metabolism, and siderophore production in this pathogen. Transcriptome analysis of the silver-exposed P. aeruginosa indicated generation of nitrosative stress and disturbance of iron homeostasis to be the major mechanisms associated with anti-Pseudomonas activity of Silversol ® . Network analysis of the differentially expressed genes in silver-treated bacterium identified ten genes as the potential molecular targets: norB, norD, nirS, nirF, nirM, nirQ, nosZ, nosY, narK1, and norE (all associated with nitrogen metabolism or denitrification). Three of them (norB, narK1, and norE) were also validated through RT-PCR.