Novel silver metformin nano-structure to impede virulence of Staphylococcus aureus

Abstract

Staphylococcus aureus is a prevalent etiological agent of health care associated and community acquired infections. Antibiotic abuse resulted in developing multidrug resistance in S. aureus that complicates treatment of infections. Targeting bacterial virulence using FDA approved medication offers an alternative to the antibiotics with no stress on bacterial viability. Using nanomaterials as anti-virulence agent against S. aureus virulence factors is a valuable approach. This study aims to investigate the impact of metformin (MET), metformin nano (MET-Nano), silver metformin nano structure (Ag-MET-Ns) and silver nanoparticles (AgNPs) on S. aureus virulence and pathogenicity. The in vitro results showed a higher inhibitory activity against S. aureus virulence factors with both MET-Nano and Ag-MET-Ns treatment. However, genotypically, it was found that except for agrA and icaR genes that are upregulated, the tested agents significantly downregulated the expression of crtM, sigB, sarA and fnbA genes, with Ag-MET-Ns being the most efficient one. MET-Nano exhibited the highest protection against S. aureus infection in mice. These data indicate the promising anti-virulence activity of nanoformulations especially Ag-MET-Ns against multidrug resistant S. aureus by inhibiting quorum sensing signaling system.

Keywords: Multidrug resistant S. aureus; Quorum sensing inhibition; Silver metformin nanostructure; Virulence.

Fig. 1

A Size distribution of Ag-MET-Ns at 66 nm, B Zeta potential of Ag-MET-Ns, C FT-IR of Metformin, MET-Nano, AgNPs and Ag-MET-Ns, D TEM image of Ag-MET-Ns and E image of Ag-MET-Ns stabilized form

Fig. 2

Inhibition of biofilm formation in S. aureus by 1/10 MICs of the tested agents. Optical density was measured at 570 nm. Significant reduction of biofilm formation was found with 1/10 MICs of the tested inhibitors in the tested bacteria compared to controls. The data shown represent the means ± standard errors. *P < 0.05, ns; non-significant

Fig. 3

Inhibition of Staphyloxanthin pigment production by 1/10 MICs of the tested agents. The pigment was extracted with methanol from treated and untreated bacterial cells and the yellow pigment was measured at OD 450 nm. The data shown represent the means ± standard errors. *; significant P < 0.05, ns; non-significant

Fig. 4

Downregulation of S. aureus QS genes by tested agents. A crtM, B sigB, C agrA, D sarA, E icaR and F fnbA using sub-MICs of the tested agents compared to controls. The data shown are the means ± standard errors of three biological experiments with three technical replicates each. *P < 0.05, ns; non-significant

Fig. 5

Bacterial load reduction by tested agents. S. aureus ATCC 6538 CFUs recovered from livers (A) and kidneys (B) of mice tissues 24 h post-infection. Bars represent mean log CFUs/g of organ tissue. The bacterial load was calculated and expressed as means ± standard errors. *P < 0.05