Bacterial biofilm formation in healthcare is a significant problem in medicine. Biofilm formation by bacteria causes higher resistance to antimicrobials due to the decrease of antimicrobial penetration and easier exchange of resistance genes between bacteria. Therefore, biofilm formation is regarded as an essential pathogenicity determinant and the resulting infections are challenging to treat [
20]. The world spread of antibiotic resistance has increased the need to develop new antimicrobial agents. Ag-NPs have gained much attention as a suitable option for eradicating biofilms and antimicrobial agents [
21]. The key cause of antibacterial behavior of such NPs could be attributed for the charge transfer mechanisms taking place between bacteria and the NPs. For the reason that of these characteristics such as, coating/capping, particle composition, dissolution rate, efficiency of ion release, size distribution, particle reactivity in solution, size, shape, particle morphology and agglomeration, Ag-NPs have been used widely in the health care industry, and in food storage, biomedical, and environmental applications. We accomplished a first antimicrobial assessment of synthesized Ag-NPs and glutathione-stabilized silver nanoparticles (GSH–Ag-NPs) by determination of MIC and MBC against
P. aeruginosa strains. The obtained results prove a significant antibacterial activity of Ag-NPs and GS–Ag-NPs with bactericidal effects at the concentration of means 1024 and 256 µg/ml against
P. aeruginosa strains, respectively (Table
2). This demonstrates the findings obtained by other researchers, which showed Ag is a potent antibiotic against a wide range of bacteria at a very low concentration without having any damaging effect on body tissues [
22,
23]. Sondi et al. showed microorganisms treated with Ag-NPs exhibited the accumulation of Ag-NPs in the cell wall and the formation of “pits” in the bacterial cell walls, ultimately leading to cell death [
24]. Kim et al. investigated the efficiency of the antimicrobial effects of Ag-NPs against yeast,
Staphylococcus aureus and
E. coli. The results show that at low concentrations of Ag-NPs, the inhibition of growth was observed in yeast,
E. coli and
S. aureus [
25]. Silvan et al. evaluated the antimicrobial effectiveness of GSH–Ag-NPs against multidrug resistant (MDR)
Campylobacter strains. The results obtained showed that GSH–Ag-NPs were highly effective against
Campylobacter strains tested; the findings of this study confirm our results [
26]. Thus, a covering of glutathione (GSH) increases the solubility and the capability of AgNPs to interact with the environment [
23]. Also, the antimicrobial effect of Ag-NPs is due to release of Ag
+ ions from Ag-NPs, which make an additional involvement to the bactericidal effect. Indeed, Ag-NPs where Ag
+ is present in the Ag
0 form also contain small concentrations of Ag+, and both Ag+ and Ag
0 contribute to the antibacterial activity [
26]. Researchers claim the antibacterial activity of the NPs may be due to the active permeability of bacterial cells through the cell wall layers or its charges. The antibacterial activity studies have demonstrated that NPs may enter the cell and attachment to cell receptors causing intracellular disintegration leading to cell death and inhibition of essential metabolic enzymes resulting in disruption of bacterial cell reproduction and respiration. Ag-NPs antibacterial mechanism works by inhibiting O
2 metabolism, which finally kills the microbes in a very short time [
27]. Moreover, it has been reported that Ag-NPs could efficiently reduction bacterial biofilm biomass [
20]. These findings indicate that the antibiofilm activity of 512 μg/ml of Ag-NPs and 256 μg/ml GSH–Ag-NPs could slightly degradation bacterial biofilm (Table
3). These findings are very similar to Mohanty et al.’s report that tested anti-biofilm activities of varying concentrations of Ag-NPs against
P. aeruginosa that reported a reduction in biofilm formation by
P. aeruginosa [
28]. The antibiofilm activity of Ag-NPs has been demonstrated in a number of studies such as Sondi et al., Montazeri et al., Besinis et al., Gurunathan et al., Kalishwaralal et al., have demonstrated the potential anti-biofilm activity Ag-NPs against Gram-negative and Gram-positive bacterial [
20,
29‐
31]. Franci et al. demonstrated that Ag-NPs exhibit effective biofilm inhibition of against
Pseudomonas putida biofilms [
32]. Ramasamy et al. exhibited that antibiofilm Ag-NPs decrease the biofilm formation by
P. aeruginosa [
33], Shafreen et al. reported for Ag-NPs an MIC of 300 ng/ml against a biofilm formed by
E. coli [
34].
In this study, we showed that exposure of
P. aeruginosa strains to ½ MIC concentration of GSH–Ag-NPs significantly reduced expression of both
las I and
las R genes reduced compared to the control sample, which could be regarded as the main cause of biofilm inhibition between
P. aeruginosa strains (
P < 0.05). Our results showed that GSH–Ag-NPs not only reduced biofilm formation ability of
P. aeruginosa strains, but also reduced the expression of the main genes associated with biofilm formation. Hentzer et al. wherein HFs have shown antiquorum-sensing activity in
P. aeruginosa by inhibiting the expression of
fabH2 gene, our results are consistent with this the report [
36]. Nejabatdoust et al. showed that functionalization of ZnO NPs with Tsc could significantly increase efficiently reduced expression of the major efflux pump genes in MDR
S. aureus strains [
37]. Consequently, penetration of Ag-NPs into the bacterial cells could interrupt several cellular functions including gene expression. In other words, the NPs inhibit cytoplasmic proteins via direct attachment which describe the reduced expression of biofilm-associated genes. Montazeri et al. reported that at sub-inhibitory concentration of Ag-NPs conjugated to thiosemicarbazide reduced expression of
ica A and
ica D genes the biofilm formation related between methicillin resistance
S. aureus, the results from this study support the finding [
20]. In another study, Gheidar et al., showed that exposure to Ag-NPs reduced the expression of
fnbA and
fnbB genes [
38]. In addition to the all the mentioned mechanisms of biofilm inhibition in
P. aeruginosa, internalization of the NPs into the bacterial cells and inhibition of cellular components may affect expression of a different set of biofilm association genes, which need further research.