Glycerol induces reuterin production and decreases Escherichia coli population in an in vitro model of colonic fermentation with immobilized human feces

Lactobacillus reuteri ATCC 55730 is a probiotic strain that produces, in the presence of glycerol, reuterin, a broad‐spectrum antimicrobial substance. This strain has been shown to prevent intestinal infections in vivo ; however, its mechanisms of action, and more specifically whether reuterin production occurs within the intestinal tract, are not known. In this study, the effects of L . reuteri ATCC 55730 on intestinal microbiota and its capacity to secrete reuterin from glycerol in a novel in vitro colonic fermentation model were tested. Two reactors were inoculated with adult immobilized fecal microbiota and the effects of daily addition of L . reuteri into one of the reactors ( c .10 8  CFU mL −1 ) without or with glycerol were tested on major bacterial populations and compared with addition of glycerol or reuterin alone. The addition of glycerol alone or with L . reuteri increased numbers of the Lactobacillus–Enterococcus group and decreased Escherichia coli . The addition of reuterin significantly and selectively decreased E . coli without affecting other bacterial populations. The observed decrease in E . coli concentration during the addition of glycerol (in presence or absence of L . reuteri ) could be due to in situ reuterin production because 1,3‐propanediol, a typical product of glycerol fermentation, was detected during the addition of glycerol.