Can glycerol reduce E. coli populations in a laboratory model of the human colon?

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Lactobacillus reuteri ATCC 55730 is a probiotic strain that produces reuterin, a broad-spectrum antimicrobial substance, in the presence of glycerol. This strain has been shown to prevent intestinal infections in vivo, but its mechanisms of action—and specifically whether it produces reuterin within the intestinal tract—are not known.

The study tested the strain’s effects on intestinal microbiota and its capacity to secrete reuterin from glycerol in a novel in vitro colonic fermentation model. Two reactors were inoculated with immobilized adult fecal microbiota. The researchers tested the effects on major bacterial populations of adding L. reuteri daily to one reactor, at approximately 10⁸ CFU mL⁻¹, with or without glycerol. They compared these effects with those of adding glycerol alone or reuterin alone.

Adding glycerol alone or together with L. reuteri increased numbers of the Lactobacillus-Enterococcus group and decreased Escherichia coli. Adding reuterin significantly and selectively decreased E. coli without affecting other bacterial populations.

During glycerol addition, the researchers detected 1,3-propanediol, a typical product of glycerol fermentation. They therefore suggested that the decrease in E. coli concentration during glycerol addition, with or without L. reuteri, could be due to reuterin production within the model.