Effects of zinc supplementation on Shiga toxin 2e-producing Escherichia coli in vitro.

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.

[Evaluation of antifungal effects of a traditional medicine containing 17 components on Trichophyton verrucosum and Malassezia pachydermatis by microdilution].

The minimum inhibitory concentration(MIC)of a traditional medicine containing 17 components against 9 strains of Trichophyton verrucosum and 13 strains of Malassezia pachydermatis was determined using a method recommended by the Clinical and Laboratory Standards Institute(CLSI). We also measured the MIC of each of the 17 components using the same method, and identified the main antifungal components.In order to evaluate MIC as a parameter of the antifungal effects using the microdilution method, we prepared 10% working solutions from 10% (w/v)medicines. The geometric mean MIC of the medicinal extract against T. verrucosum was 2.51%, and that against M. pachydermatis was 2.25%. The components that exhibited antifungal effects were Rheum palmatum, Glycyrrhiza uralensis, Magnolia obovata, Phellodendron amurense, and Geranium thunbergii.