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: The pronounced increase in biofilm formation of V. cholerae treated with ZnO-NPs was unexpected. However, it was recently shown that adenylyl cyclases can be inhibited by Zn and consequently a sublethal concentration of ZnO-NPs could decrease cAMP levels in V. cholerae (Klein et al., 2002, 2004). Besides others, the second messenger cAMP negatively effects biofilm formation as well as expression of the cholera toxin and the major colonization factor TCP in V. cholerae (Fong and Yildiz, 2008; Skorupski and Taylor, 1997a, 1997b). Thus, treatment with sublethal concentrations of ZnO-NPs could cause adverse effects and induce biofilm formation and virulence. Interestingly, the outer membrane porin OmpT is positively regulated by this second messenger and lack of cAMP completely abolishes OmpT expression (Li et al., 2002). In order to confirm the hypothesis of adenylyl cyclase inhibition by ZnO-NPs, the outer membrane (OM) proteins were isolated from V. cholerae cultures grown in absence or presence of sublethal concentrations of ZnO-NPs, Ag-NPs or zinc- and silver nitrate solutions. Subsequently, these OM preparations were subjected to immunoblot analysis (Fig. 6). Kang staining and detection of OmpU by immunoblot served as loading controls (Fig. 6A and C). While no difference in the abundance of OmpU was observed, all preparations grown in presence of ZnO-NPs or zinc nitrate exhibited only low levels of OmpT (Fig. 6B, lane 2, 3, 4). This result strengthens the hypothesis that treatment with ZnO-NPs inhibits the adenylyl cyclase activity resulting in low cAMP levels.
Affiliation: University of Graz, Institute of Molecular Biosciences, BioTechMed-Graz, Humboldtstrasse 50, A-8010 Graz, Austria; South Valley University, Faculty of Science, Qena, Egypt.