In Vitro Evaluation of Dietary Fiber Anti-Infectious Properties against Food-Borne Enterotoxigenic Escherichia coli

Abstract

Dietary fibers have well-known beneficial effects on human health, but their anti-infectious properties against human enteric pathogens have been poorly investigated. Enterotoxigenic Escherichia coli (ETEC) is the main agent of travelers’ diarrhea, against which targeted preventive strategies are currently lacking. ETEC pathogenesis relies on multiple virulence factors allowing interactions with the intestinal mucosal layer and toxins triggering the onset of diarrheal symptoms. Here, we used complementary in vitro assays to study the antagonistic properties of eight fiber-containing products from cereals, legumes or microbes against the prototypical human ETEC strain H10407. Inhibitory effects of these products on the pathogen were tested through growth, toxin production and mucus/cell adhesion inhibition assays. None of the tested compounds inhibited ETEC strain H10407 growth, while lentil extract was able to decrease heat labile toxin (LT) concentration in culture media. Lentil extract and specific yeast cell walls also interfered with ETEC strain H10407 adhesion to mucin beads and human intestinal cells. These results constitute a first step in the use of dietary fibers as a nutritional strategy to prevent ETEC infection. Further work will be dedicated to the study of fiber/ETEC interactions within a complex gut microbial background.

Lentils and Yeast Fibers: A New Strategy to Mitigate Enterotoxigenic Escherichia coli (ETEC) Strain H10407 Virulence?

“…The specific yeast cell wall from Saccharomyces cerevisiae AQP 12,260 and the raw green lentils were provided by Lallemand SAS (Blagnac, France) and HARi&CO (Lyon, France), respectively. The lentils were prepared according to their usual household consumption and were extracted by a digestion step followed by ethanol precipitation, as previously described [ 19 ]. Briefly lentils were boiled (30 min), washed in sterile distilled water, ground at maximum speed in a blender 8010S (Waring, Stamford, CT, USA) until homogeneity, and filtered through a 0.9 mm diameter pore filter.…”

“…The LT concentration was assayed by cultivating ETEC strain H10407 in Casamino acids-yeast extract (CAYE) medium (37 °C, 100 rpm) with or without fiber-containing products at various concentrations (ranging from 0.0625 to 8 g·L −1 ). After overnight culture, the medium was centrifuged (3000× g , 5 min, 4 °C), and toxin concentrations were measured in the supernatant by GM-1 ELISA assay, as previously described [ 19 ]. Pure LT toxin detection inhibition assays were also carried out as aforementioned with pure LT-Cholera B toxin sub-unit (Sigma-Aldrich, Saint-Louis, MO, USA) added in CAYE medium at a concentration of 500 ng·mL −1 without ETEC bacteria.…”

“…Antibiotic therapy is often prescribed to patients, although it is not routinely recommended due to the rise in antimicrobial resistance and potential side effects on human health [ 15 ]. Potential alternative strategies are therefore being investigated, including bacteriophages [ 16 ], probiotics [ 17 ], or less well known dietary fibers [ 18 , 19 ].…”

“…More recently, in vitro studies have also shown the antagonistic properties of fibers against various enteric bacterial pathogens, mostly through a direct bacteriostatic effect [ 27 , 28 , 29 , 30 ], anti-adhesion properties on intestinal cells, or a decoy for pathogen/toxin binding to mucosal polysaccharides [ 19 , 31 , 32 , 33 , 34 ]. The effects from dietary fiber can also be indirectly mediated by gut microbiota modulation, e.g., by supporting probiotic species showing anti-infectious properties [ 35 ].…”

“…Only milk oligosaccharides and plantain soluble fibers were proven to reduce the adhesion of ETEC strains Pb-176, CECT 685, and C410 to human Caco-2 intestinal epithelial cells [ 18 , 38 , 39 ]. Facing this lack of data, we previously conducted a short screening program to select the most promising fiber-containing products among eight candidates, i.e., a homemade lentil extract and specific yeast cell walls from Saccharomyces cerevisiae AQP 12,260 [ 19 ].…”