A non-specific effect of orally administered Escherichia coli.

A number of genetically modified bacteria able to deliver a therapeutic gene into target cells has already been tested. Apart from the expected effects of bacterial therapy, the therapeutic bacterial strain also mediates a non-specific effect independent of the gene to be delivered. In this regard, we have recently shown that oral administration of the bacterial strain Escherichia coli XL1-Blue via gastric gavage to rats leads to a non-specific decrease in expression of vascular endothelial growth factor (VEGF) in intestinal wall without corresponding changes in other parameters. We tried to adopt a model of intestinal ischemia and to treat the subsequent hypoxic condition using a strain carrying the effector plasmid encoding hypoxia-inducible factor 1 alpha (HIF-1alpha), as well as the helper plasmid encoding invasion and listeriolysin O. However, the model was ineffective, as obvious from macroscopic and molecular observations. We hypothesize that a competitive behavior of the administered strain in the intestinal microbiota leads to a decrease in activity of HIF-1alpha and reduction in expression of VEGF. Also, a functional disease model would be necessary for the invasion-expressing therapeutic strain to be effective. A different approach using bacterial protein delivery would possibly circumvent these bactofection-related problems.