Colostrum from healthy Brazilian women inhibits adhesion and contains IgA antibodies reactive with Shiga toxin-producing Escherichia coli

Although Shiga toxin-producing Escherichia coli (STEC) has been isolated in Brazil, severe manifestations of the infection, such as haemorrhagic colitis and haemolytic-uraemic syndrome, are extremely rare in our population. Enteropathogenic Escherichia coli (EPEC) is the main aetiological agent of acute infantile diarrhoea in Brazil. There are many similarities between STEC and EPEC, such as the ability to produce attaching and effacing (A/E) lesions and some virulence-associated factors. Our aim was to investigate the presence of anti-STEC antibodies in healthy people living in an EPEC endemic area. Colostrum samples collected from 51 women living in low socio-economic conditions were analysed. Two STEC strains: O111:H- (Stx1) and O157:H7 (Stx2), and one EPEC strain (O111:H-) were used in the bacterial adhesion assays to HEp-2 cells, in the Stx1 and Stx2 cytotoxicity assays on Vero cells, in immunoblotting and in ELISA assays. All the samples strongly inhibited the adhesion of the three strains and contained SIgA antibodies reactive with antigens of EPEC O111:H-, STEC O111:H- and STEC O157:H7, mainly STEC and EPEC 94 kDa adhesin intimin. High titres of anti-LPS O111 antibodies were found in many samples. Nevertheless, the cytotoxic effect of both Stx1 and Stx2 on Vero cells was not neutralised by any sample. Conclusion: Our results suggest that Brazilian people may be exposed to Shiga toxin-producing Escherichia coli more frequently than previously thought or alternatively there may be a cross reactive immunity between enteropathogenic Escherichia coli and Shiga toxin-producing Escherichia coli.