Zn is an essential element for microorganisms and higher organisms because it is involved in many vital cellular reactions at its low endogenous concentrations, acting as a cofactor needed for catalytic and structural activities [36, 37]. Zn ion concentrations of 10-5-10-7 M are required for optimal bacterial growth of most microorganisms in vitro [38]. However, it is claimed that high zinc ion concentrations may have some antibacterial properties [39]. Zn concentration is regulated under physiological conditions by several transporters [40, 41], so that Zn ions are essentially nontoxic to higher organisms. Although homeostasis regulates Zn uptake by cells, it does not control zinc adsorption to cell membranes. Among the mechanisms proposed for the antimicrobial effect of Zn, a direct interaction with microbial membranes leading to membrane destabilization and enhanced permeability has been discussed. Cellular internalization of Zn and the production of active oxygen species have been proposed in earlier studies. Increase of Zn concentrations above optimal levels perturbs its homeostasis and allows its entry inside cells, so that Zn starts being cytotoxic to prokaryotes above a concentration of ∼10−4 M [38,
Zn is an essential element for microorganisms and higher organisms because it is involved in many vital cellular reactions at its low endogenous concentrations, acting as a cofactor needed for catalytic and structural activities [36, 37]. Zn ion concentrations of 10-5-10-7 M are required for optimal bacterial growth of most microorganisms in vitro [38]. However, it is claimed that high zinc ion concentrations may have some antibacterial properties [39]. Zn concentration is regulated under physiological conditions by several transporters [40, 41], so that Zn ions are essentially nontoxic to higher organisms. Although homeostasis regulates Zn uptake by cells, it does not control zinc adsorption to cell membranes. Among the mechanisms proposed for the antimicrobial effect of Zn, a direct interaction with microbial membranes leading to membrane destabilization and enhanced permeability has been discussed. Cellular internalization of Zn and the production of active oxygen species have been proposed in earlier studies. Increase of Zn concentrations above optimal levels perturbs its homeostasis and allows its entry inside cells, so that Zn starts being cytotoxic to prokaryotes above a concentration of ∼10−4 M [38,