Neutralizing properties of human milk against shiga toxin type 2

Abstract

Shiga toxin (Stx) producing Escherichia coli (STEC) is a foodborne pathogen responsible for Hemolytic Uremic Sindrome (HUS). Stx is the main virulence factor responsible for this disease and Stx type 2 (Stx2) has been associated with more severe cases affecting mainly children under 5 years of age. Breastfeeding is one of the least cost-effective public health tools to protect the newborn from diarrhea and its effectiveness can be attributed to different bioactive compounds transmitted through milk. We have previously demonstrated that rats immunized against Stx2 can transfer through lactation protection against a lethal dose of Stx2 to their offspring. In thiswork we aim to evaluate whether human milk from human healthy donors may have protective properties against Stx2. Human milks (n=107) were collected under informed consent at the National Hospital Prof. Alejandro Posadas by the manual method from healthywomen (18-45 years). After collection, milks were stored at 20°C until used. Milks were delipidated by centrifugation at 3000 rpm for 45 min. Supernatant was collected from samples and used for the evaluation of: 1) Neutralizing capacity of Stx2 in vitro on Vero cells, 2) Total protein content by the BCA kit 3) Total IgA content by radial immunodiffusion (RID) and 4) Ig Anti STEC titer by ELISA. Collected milk samples showed a mean of 229 mg/dL of total IgA levels (range: 10-675 mg/dL). Total protein content of samples was heterogeneous and ranged from 5.5 to 166.5 mg/ml. Fourteen milksamples (14/107; 13%) showed neutralizing properties against Stx2 in vitro. When comparing IgA levels and protein content of positive and negative samples for Stx2 neutralization, no significative differences were observed. Neutralizing capacity of Stx2 has no correlation with high Ig titer against STEC. These results indicate that some human milk may have neutralizing properties against Stx2. These data may be important for HUS prevention of newborn by promoting breastfeeding.