Clover Honey Limits Survival of Enterotoxigenic Escherichia coli in an In Vitro Gastric Model and Reduces In Vitro Fermentation pH of Small Intestine Microbes.

BACKGROUND

Honey has well-described antimicrobial properties in wound healing, but little is known about its effects within the gastrointestinal tract.

OBJECTIVE

We used in vitro gastric digestion and fermentation of clover honey to investigate its potential interactions with small intestine bacteria (SIB), the foodborne pathogen enterotoxigenic Escherichia coli (ETEC), and small intestine epithelial cells.

METHODS

In vitro gastric digestions of sterile-filtered honey, and a simple sugar control were performed with 1 × 108 colony-forming units (CFU)/mL ETEC H10407. ETEC CFU and pH were measured, and the resulting digesta were added to batch fermentations with SIB, in the form of a mock community or ileal aspirate from 6 healthy donors. SIB fermentations were characterized by 16S rRNA amplicon sequencing and application of fermentation supernatants to mature Caco-2 cell monolayers for analysis of changes in transepithelial electrical resistance (TEER) and interleukin (IL)-8 production. Differential abundance of bacterial taxa detected by 16S rRNA sequencing between the honey and sugar conditions was tested using an Analysis of Compositions of Microbiomes with Bias Correction 2. Differences in ETEC CFU, media pH, and changes in TEER and IL-8 production between the honey and sugar conditions were tested by linear mixed effects modeling with post hoc least-squares means analysis.

RESULTS

Under pH 2.5 in vitro gastric digestion conditions, ETEC CFU decreased significantly (P < 0.0001) more in the presence of clover honey (0.0035% input) than in a sugar control (0.036% input). The pH of SIB fermentation media was significantly reduced (P < 0.0001) with digested honey relative to sugar. Honey fermentation supernatant from human ileal communities challenged with ETEC elicited a greater improvement in TEER (3.68 compared with -0.80, P = 0.0479) relative to the same fermentations performed with control.

CONCLUSIONS

Honey limits the survival of ETEC H10407 within an in vitro gastric environment at low pH. Clover honey may also impart decreased pH and potential improvement in in vitro epithelial cell barrier integrity in the presence of a pathogen.