Bioengineered bugs expressing oligosaccharide receptor mimics: toxin-binding probiotics for treatment and prevention of enteric infections

Abstract

Many microbial pathogens recognize oligosaccharides displayed on the surface of host cells as receptors for toxins and adhesins. These ligand-receptor interactions are critical for disease pathogenesis, making them promising targets for novel anti-infectives. One strategy with particular utility against enteric infections involves expression of molecular mimics of host oligosaccharides on the surface of harmless bacteria capable of surviving in the gut. This can be achieved in Gram-negative bacteria by manipulating the outer core region of the lipopolysaccharide (LPS) through expression of cloned heterologous glycosyltransferases. The resultant chimeric LPS molecules are incorporated into the outer membrane by the normal assembly route and presented as a closely packed 2-D array of receptor mimics. Several such "designer probiotics" have been constructed, and these bind bacterial toxins in the gut lumen with very high avidity, blocking their uptake by host cells and thereby preventing disease.

Keywords: Shiga toxin; cholera; lipopolysaccharide; oligosaccharide receptor; toxin neutralization; travelers' diarrhea.

Figure 1

Specific binding of toxins to cognate receptor mimic probiotics. Suspensions of the E. coli host strain CWG308, or derivatives expressing mimics of Gb₃ (A) or GM1 (B), fixed on poly-L-lysine-treated slides, were reacted with Texas Red-labelled Shiga toxin B subunit (StxB) (A) or cholera toxin B subunit (CtxB) (B). Slides were examined using a BioRad MRC 600 Dual-Fluorescence Confocal microscope.