Sub-lethal concentration of a colloidal nanosilver formulation (Silversol®) triggers dysregulation of iron homeostasis and nitrogen metabolism in multidrug resistant Pseudomonas aeruginosa

Abstract

Background Pseudomonas aeruginosa is a notorious pathogen. Its multidrug resistant strains are listed among priority pathogens against whom discovery of novel antibacterial agents and, elucidation of new anti-pathogenicity mechanisms are urgently warranted. This study describes multiple antibacterial effects of a colloidal nano-silver formulation- Silversol® against a multi-drug resistant strain of P. aeruginosa. Results Minimum inhibitory concentration (MIC) of Silversol® 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 (pyocanin 82%↓; pyoverdine 48%↑), exopolysaccharide synthesis (76%↑) and biofilm formation, susceptibility to antibiotics (streptomycin and augmentin), protein synthesis and export (65%↑), nitrogen metabolism (37%↑ nitrite accumulation), and siderophore production in this pathogen. Network analysis of the differentially expressed genes in the transcriptome of the silversol-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. Conclusions Generation of nitrosative stress and disturbance of iron homeostasis were found to be the major mechanisms associated with anti-Pseudomonas activity of Silversol®.

Silversol®(a colloidal nanosilver formulation) inhibits growth of antibiotic-resistantStaphylococcus aureusby disrupting its physiology in multiple ways

“…These results indicate that Silversol could penetrate the biofilm matrix to exert its effect on metabolic activity/ viability of constituent cells. Reduced biofilm formation and decrease in biofilm viability in presence of Silversol was earlier reported by us in case of Pseudomonas aeruginosa too (Gajera et al, 2023b). This anti-biofilm activity of Silversol is important considering that bacterial biofilms exert antibiotic tolerance at higher level, and biofilm infections are more difficult to treat (Zhao et al, 2023).…”

“…However, Silversol's growth-inhibitory action against other pathogens may or may not stem from same mode of action. For example, in our recent study (Gajera et al, 2023b) describing Silversol's anti-P. aeruginosa activity, arginine metabolism was not found to be among the physiological traits attacked by this colloidal silver formulation. It is possible, that despite being a broad-spectrum antibacterial agent, mode of action of Silversol against different pathogenic bacteria may differ more or less.…”

“…Biofilm formation is an important virulence trait, and hence effect of Silversol on biofilm forming ability of S. aureus, as well as on pre-formed biofilm was investigated through four different biofilm assays using methodology described in our previous publication (Gajera et al, 2023b). A flow diagram depicting all the biofilm assays is provided in Figure 1, wherein biofilm quantification was achieved through crystal violet assay (Hirshfield et al, 2009), and biofilm viability was assessed through MTT assay (Trafny et al,2013).…”

Silversol® (a Colloidal Nanosilver Formulation) Inhibits Growth of Antibiotic-Resistant Staphylococcus aureus by Disrupting Its Physiology in Multiple Ways

“…Biofilm formation is an important virulence trait, and hence the effect of Silversol on the biofilm-forming ability of S. aureus , as well as on pre-formed biofilm was investigated using four different biofilm assays using the methodology described in our previous publication [ 37 ]. A flowchart illustrating all the biofilm assays is provided in Figure 1 , wherein biofilm quantification was carried out using crystal violet assay [ 38 ], and biofilm viability assessment was conducted using MTT assay [ 39 ].…”

Green Synthesis of Narrow-Size Silver Nanoparticles Using Ginkgo biloba Leaves: Condition Optimization, Characterization, and Antibacterial and Cytotoxic Activities

“…Additionally, the primary mechanism of the antibacterial effect of a colloidal nanosilver formulation called Silversol against P. aeruginosa involved the disruption of iron homeostasis and induction of nitrosative stress. Importantly, Silversol selectively targeted proteins in P. aeruginosa without affecting beneficial bacteria found in humans, especially the human gut, making it a potential candidate for antibiotic development [63]. Moreover, some studies have investigated the synergistic antibacterial effects of combining nanosilver and antibiotics to mitigate the development of bacterial resistance.…”