In a study published today in mBio, researchers from the University of Cincinnati assessed how Nissle—a strain of Escherichia coli that is harmless to the intestinal tissue—may provide defense against enterohemorrhagic E. coli or EHEC. EHEC is responsible for the production of Shiga toxin, which afflicts millions and kills thousands of people every year, most of whom are children. There are currently no approved therapies for EHEC infection, and antibiotics may increase Shiga toxin production.
While E.coli is commonly associated with the few strains that can cause lethal symptoms, the commensal strain Nissle has been used as a probiotic for centuries. In recent years it’s even been used for ulcerative colitis and IBS treatment.
To study the relationship between commensal and pathogenic E.coli, researchers injected human intestinal organoids (HIOs) with Nissle and observed that its effects were harmless. They then injected HIOs with EHEC and saw that the pathogen quickly broke down the epithelial barrier in the HIOs. Afterward, they pre-treated HIOs with Nissle and waited 12 hours before exposing the organoids to EHEC.
The team found that although EHEC proliferated in the tissue, it was unable to destroy the epithelial barrier. Nissle proved to be protective, although its population declined rapidly. "Basically, the Nissle was killed by the pathogenic bacteria, but it made the intestine able to withstand damage better," said co-author Alison Weiss.
Their findings also indicate that Nissle’s protective effects come not from inhibiting the pathogenic strains, but from harnessing the defense mechanisms within the cell itself and that the probiotic might reduce the severity of EHEC infections. Weiss adds that more research is needed to better understand the interactions of bacterial species in real-world settings, but that HIOs hold invaluable potential as models for better understanding intestinal conditions.