NutriClay Zn Harbors Bioavailable Zinc and Suppresses Multidrug-Resistant Salmonella Choleraesuis

Abstract

Pharmacological doses of zinc oxide (ZnO), far in excess of the nutritional requirement for zinc, are commonly added to weanling swine feed to suppress enterotoxigenic bacteria and thereby support piglet weight gains. However, excessive ZnO in the diet has come under scrutiny due to concerns that excreted zinc may accumulate beyond safe levels within topsoil and water supplies, as well as foster antibiotic drug resistance in bacterial pathogens that could then infect livestock and/or humans. Indeed, multidrug-resistant (MDR) Salmonella have been isolated from swine feces, focusing attention on new technologies to protect swine (and ultimately humans) while reducing dietary zinc toward the nutritional requirement. We hypothesized that NutriClay^Zn (an edible Generally Recognized As Safe substance consisting of low-dose ZnO immobilized on montmorillonite clay) could suppress MDR Salmonella, provide bioavailable zinc, and serve as a novel feed ingredient for weanling swine. NutriClay^Zn dose–response efficacy and thermal stability were assessed in cultures of MDR Salmonella Choleraesuis. Dissociated elemental zinc was measured under simulated gastrointestinal conditions. NutriClay^Zn consumption was assessed via ad libitum feeding, with bioavailable zinc calculations according to weanling swine treatment group intakes. Salmonella Choleraesuis (resistant to quinolone, sulfonamide, and aminoglycoside antibiotics) was susceptible to growth inhibition by heat-stable NutriClay^Zn. Under simulated gastrointestinal conditions, 22.8 µg of elemental zinc were released per milligram NutriClay^Zn. Furthermore, the rate at which weanling swine consumed NutriClay^Zn-containing feed (0.6 kg/day) supports fulfillment of the nutritional zinc requirement. These findings encourage future MDR Salmonella pathogen challenge trials, designed with NutriClay^Zn replacing pharmacological ZnO for control of enterotoxigenic bacteria in swine, as well as potentially eliminating the zinc component of mineral premixtures that are currently added to feed for nutritional purposes.

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