Results of the present investigation indicate that both, Zn-gluconate and Zn-sulphate, inhibit the growth of G. lamblia trophozoites in vitro. To date, there are no reports about the effect of Zn on gastrointestinal parasites. Very few studies have so far been conducted on the antibacterial effect of various salts of Zn on enteric pathogens. An in vitro study conducted by Surjawidjaja et al. (2003) showed that Zn-sulfate at concentrations between 1.2 and 1.8 mg/ml inhibited the growth in enteric pathogens commonly associated with diarrheal disease (Salmonella typhi, Salmonella groups A, B, C, D and E, Escherichia coli, Enterobacter, Shigella and Vibrio cholera). Our results seem to indicate that Giardia is more sensitive to Zn than these enteric
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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,