Immunization of pregnant cows with Stx2 induces high levels of specific colostral antibodies able to neutralize the pathogenicity of Stx2-producing E. coli O157:H7

ALBANESE, ADRIANA; RABINOVITZ, BETTINA; FERNANDEZ BRANDO, ROMINA; PALERMO, MARINA S.; CATALDI, ANGEL A.; MERCADO, ELSA C.; IBARRA, CRISTINA

New York

Congreso; 9th International Symposium on Shiga Toxin (Verocytotoxin)-producing Escherichia coli Infections (VTEC 2015); 2015

VTEC

Introduction. Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is responsible for intestinal disease and hemolytic uremic syndrome (HUS), a serious systemic complication frequently associated with Shiga toxin type 2 (Stx2). The aim of this study was to evaluate the ability of bovine hyperimmune colostral antibody against Stx2 to prevent the pathogenicity of EHEC O157:H7.Methods. Three pregnant cows were intramuscular immunized at 40 and 20 days before delivery with 100 g of inactivated Stx2 mixed with 1 mL of mineral oil-based adjuvant. Colostrum was obtained within the first 24 h after parturition and the IgGs were purified by affinity chromatography. The neutralizing capacity of Stx2 was determined for viability assay in Vero and HTC-8 cell lines. Colon loops of male SD rats were incubated overnight with either Stx2 or Stx2 pre-incubated 30 min at 37ºC with IgG from colostrum of immunized or non-immunized cows. Colon loops were inoculated with EHEC O157:H7 grown to exponential phase with or without preincubation with hyperimmune colostral IgG. Colon loops were rapidly removed, measured for length and fluid content, and analyzed on optic microscopy. BalB-c weaned mice were inoculated intragastrically with lethal dose (2.4x1010 CFU/Kg) of EHEC O157:H7. Some mice received one or two doses of IgGs (7.5 mg/dose) 1 h before and 2 h after EHEC challenge. The EHEC O157:H7 used was the strain 125/99 Stx2+ belonging to the hypervirulent clade 8 isolated from a pediatric HUS patient.Results and Discussion. High titers (1/5000) of purified IgG antibody against Stx2 was observed in vaccinated cows using Vero and HCT-8 assays. In addition, rat colon loops treated with Stx2 or EHECO157:H7 previously incubated with hyperimmune colostral IgG prevent secretion of bloody fluid and histological alterations observed in colon loops inoculated with EHEC O157:H7. Preliminary results treating BalB-c weaned mice with hyperimmune colostral IgG by oral route showed a dose-dependent partial protection against a lethal bacterial challenge.Implications. These results suggest that the presence of neutralizing anti-Stx2 antibodies in hyperimmune bovine colostrum could be used as nutraceutics in children at risk of HUS.