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
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Mentions: Antibacterial activity of the different NPs synthesized by C. procera plant extracts against the human pathogens V. cholerae and ETEC was analyzed by minimal inhibitory concentration (MIC) and INT assays (Fig. 3). MIC was defined as the lowest concentration at which no increase of the OD600 of the pathogens was observed. However, in the absence of cell lysis the measurement of turbidity cannot distinguish between live and dead bacteria (Carroll et al., 2010). Thus, we additionally determined bacterial viability by a colorimetric INT-formazan assay, which allows detection of viable bacteria by their respiratory activity (Mann and Markham, 1998; Palomino et al., 2002). All four NPs showed reproducible, effective antibacterial activity with similar results in both assays (Fig. 3). In general, ZnO-NPs showed a slightly higher efficacy compared to Ag-NPs, with ZnO-NPs-F exhibiting the lowest MIC against both pathogens. In detail, ZnO-NPs concentrations of 1.6 × 105–1.2 × 106 per ml were sufficient for killing of V. cholerae and ETEC (Fig. 3A and B), while in case of the Ag-NPs concentration of 5 × 106–1.2 × 107 per ml were necessary (Fig. 3C and D). Within the MIC and INT assays no detectable difference compared to the LB control were observed in the presence of plant extracts alone (data not shown). Consistently, a comprehensive analysis revealed that neither the presence of leaf nor fruit extracts had a negative effect on the growth kinetics or viability of V. cholerae or ETEC in comparison to the LB control (Fig. 4). To exclude the possibility of soluble side-products with antimicrobial activity in the NPs solution, the NPs-free supernatants from NPs solutions were obtained by centrifugation and tested in the MIC/INT assay. The absence of NPs in the supernatant was confirmed by NTA. None of the NP-free supernatants derived from the four types of NPs solutions (ZnO-NPs-L, ZnO-NPs-F, Ag-NPs-L and Ag-NPs-F) exhibited any residual antimicrobial activity. Thus, the determined MIC correlates with the presence of NPs.
Affiliation: University of Graz, Institute of Molecular Biosciences, BioTechMed-Graz, Humboldtstrasse 50, A-8010 Graz, Austria; South Valley University, Faculty of Science, Qena, Egypt.