Bacteria may ward off infection

Researchers have explored the role of Lactobaccilus reuteri—a natural resident of the human gut—to protect against foodborne infection.

Their results demonstrated that this beneficial or probiotic organism, which produces an antimicrobial substance known as reuterin, may protect intestinal epithelial cells from infection by the foodborne bacterial pathogen Salmonella.

Cheryl Nickerson and her group at ASU’s Biodesign Institute, in collaboration with an international team including Tom Van de Wiele and lead author Rosemarie De Weirdt at Ghent University, Belgium, conducted the study.

It examines for the first time the effect of reuterin during the infection process of mammalian intestinal cells and suggests the efficacy of using probiotic bacteria or their derivatives in future therapies aimed at thwarting Salmonella infection.

 Intestinal infections by non-typhoidal Salmonella strains induce diarrhea and gastroenteritis, and remain a leading source of foodborne illness worldwide. Such infections are acutely unpleasant but self-limiting in healthy individuals. For those with compromised immunity however, they can be deadly and the alarming incidence of multi-drug resistant Salmonella strains has underlined the necessity of more effective therapeutics.

The use of benign microorganisms offers a promising new approach to treating infection from pathogens like Salmonella and indeed, L. reuteri has been shown to help protect against gastrointestinal infection and reduce diarrhea in children.
The origin of L. reuteri’s protective role still remains unclear. While it has been speculated that reuterin acts by regulating immune responses or competing with Salmonella for key binding sites, the current study represents the first in vitro examination of host-pathogen interactions using human intestinal epithelium in the presence of reuterin-producing L reuteri.

The results showed a reduction in the Salmonella population (without host cells) after one hour of exposure to a diluted supernatant containing reuterin. Further, the reuterin-containing ferment of L. reuteri was shown to significantly reduce adhesion, invasion and intracellular survival of Salmonella to 3-D colon cells, compared with an untreated control.

In an unexpected twist, the application of L. reuteri supernatant lacking glycerol actually stimulated adhesion, invasion and intracellular survival of Salmonella. The authors speculate that the stimulatory effect observed may have been due to low concentrations of acetic acid, previously shown to stimulate expression of Salmonella virulence-related genes.

Another interesting detail uncovered in the study is that the effects of reuterin on Salmonella’s infectious capacity are increased in the presence of host cells, suggesting that some type of synergistic protection occurs during epithelial infection, potentially involving the combined activity of reuterin and host cell gene-related responses.

While the authors stress that much work remains, particularly in terms of understanding reuterin’s role in the context of a complex gut microbiome, the results are encouraging and suggest a new avenue for fighting Salmonella infection, through the process of glycerol conversion to reuterin by L. reuteri.