Antibacterial activity of silver and zinc nanoparticles against Vibrio cholerae and enterotoxic Escherichia coli.
Bottom Line: In order to investigate new effective and inexpensive therapeutic approaches, we analyzed nanoparticles synthesized by a green approach using corresponding salt (silver or zinc nitrate) with aqueous extract of Caltropis procera fruit or leaves.Using the expression levels of the outer membrane porin OmpT as an indicator for cAMP levels, our results suggest that zinc nanoparticles inhibit adenylyl cyclase activity.Finally, we demonstrated that a single oral administration of silver nanoparticles to infant mice colonized with V. cholerae or ETEC significantly reduces the colonization rates of the pathogens by 75- or 100-fold, respectively.
Affiliation: University of Graz, Institute of Molecular Biosciences, BioTechMed-Graz, Humboldtstrasse 50, A-8010 Graz, Austria; South Valley University, Faculty of Science, Qena, Egypt.Show MeSH
Related in: MedlinePlus
Mentions: Zinc oxide and silver nanoparticles (ZnO-NPs and Ag-NPs) were synthesized according to established protocols using leaf (L) and fruit extracts (F) from C. procera (Geethalakshmi and Sarada, 2010; Hui et al., 2004; Sangeetha et al., 2011; Song and Kim, 2009), resulting in the four different types of nanoparticles ZnO-NPs-L, ZnO-NPs-F, Ag-NPs-L and Ag-NPs-F. After the addition of leaf and fruit extracts to the silver or zinc nitrate solutions, color changes appeared within 30 min indicating the completion of the reaction, which is due to the excitation of plasmon vibrations in the metal nanoparticles (data not shown). In contrast, the control silver or zinc nitrate solution without extracts showed no color change (data not shown). The intensity of colors steadily increased along the incubation period. Finally, Ag-NPs-L and Ag-NPs-F solutions exhibited a dark brown color, while solutions of Zn-NPs-L and Zn-NPs-F exhibited dark yellow color. This may be due to the excitation of the surface plasmon resonance (SPR) effect (Haes and Van Duyne, 2002) and the reduction of either AgNO3 (Mulvaney et al., 1996) or zinc nitrate (Sangeetha et al., 2011). The reduction of aqueous extracts by silver or zinc ions and the formation of each NP-type were confirmed using UV–vis spectroscopy (Fig. 1). A wavelength scans in the UV–vis spectra revealed an absorption peak at approximately λ = 340 for ZnO-NPs-L and Zn-NPs-F (Fig. 1A and B). Furthermore Ag-NPs-L and Ag-NPs-F exhibited characteristic absorption peaks at approximately λ = 370 nm as previously published (Jeeva et al., 2014) (Fig. 1C and D). The presence of Zn and Ag in the NPs solutions was confirmed by inductively coupled plasma mass spectrometry (ICP-MS), which revealed an at least 7-fold increase in case of Zn or 400-fold in case of Ag in the NPs solutions compared to the plant extracts, respectively (Table 1). The exact size distributions and concentrations of independent NP preparations used in the assays presented herein were determined by nanoparticle tracking analysis (Fig. 2). Throughout the study, each type of NP has been prepared at least three times without tremendous changes in yield or quality, suggesting a reproducible production of the NPs. In general, all NP preparations showed similar results with mean concentrations ranging from 1.65 to 3.8 × 108 NPs/ml, mode particle sizes of 88–100 nm and average particle size of 120–169 nm. The difference between mode and average particle sizes indicates a non-parametric distribution of the NPs with the majority ranging around 90–100 nm in size as well as a minor population with bigger diameters. No aggregations or debris were detected by visualization of the NPs within the nanoparticle tracking analysis (data not shown), which indicates that NP suspensions are quite pure and homogenous.
Affiliation: University of Graz, Institute of Molecular Biosciences, BioTechMed-Graz, Humboldtstrasse 50, A-8010 Graz, Austria; South Valley University, Faculty of Science, Qena, Egypt.