Swine edema disease is caused by
Shiga toxin (Stx) 2e-producing Escherichia coli (STEC). Addition of highly concentrated
zinc formulations to feed has been used to treat and prevent the disease, but the mechanism of the beneficial effect is unknown. The purpose of the present study was to investigate the effects of highly concentrated
zinc formulations on bacterial growth,
hemolysin production, and an Stx2e release by STEC in vitro. STEC strain MVH269 isolated from a piglet with
edema disease was cultured with
zinc oxide (ZnO) or with
zinc carbonate (ZnCO3), each at up to 3,000 ppm. There was no effect of
zinc addition on bacterial growth. Nonetheless, the cytotoxic activity of Stx2e released into the supernatant was significantly attenuated in the
zinc-supplemented media compared to that in the control, with the 50% cytotoxic dose values of 163.2 ± 12.7, 211.6 ± 33.1 and 659.9 ± 84.2 after 24 hr of growth in the presence of ZnO, ZnCO3, or no supplemental
zinc, respectively. The hemolytic zones around colonies grown on sheep blood
agar supplemented with
zinc were significantly smaller than those of colonies grown on control
agar. Similarly,
hemoglobin absorbance after exposure to the supernatants of STEC cultures incubated in sheep blood broth supplemented with
zinc was significantly lower than that resulting from exposure to the control supernatant. These in vitro findings indicated that
zinc formulations directly impair the factors associated with the virulence of STEC, suggesting a mechanism by which
zinc supplementation prevents
swine edema disease.