Molecular Analysis of Intestinal Microbiota Composition to Evaluate the Effect of PEG and Lactulose Laxatives in Humans

Methods using bacteriological cultures allow only 30–50 % of colonic bacterial populations to be detected. Our aim was to assess the effect of osmotic laxative administration on fecal bacteria during chronic idiopathic constipation, by a culture-independent molecular method. Forty-eight constipated patients were included in a randomized blinded trial and received either polyethylene glycol (PEG, n23) or lactulose (n25) for 28 days. Non-fermentable laxative (PEG) should not affect the bacterial groups, whereas fermentable (lactulose) could modulate them. The treatment dosage was 20 g per day for a 7-day period, then adjusted according to ef cacy for 7 days and constant from 10 to 30 g per day for 14 days. Stools were collected at d0, d21 and d28, and analyzed by quantitative dot-blot hybridization using 16S ribosomal RNA-targeted oligonucleotide probes. We used a new Bi dobacterium group speci c probe and ve other probes to monitor the dominant groups of the intestinal bacteria: Bacteroides-Prevotella-Porphyromonas, Lactobacillus-Enterococ-cus-Streptococcus, enterobacteria: Clostridium coccoides and Clostridium leptum. Lactulose and PEG administration were associated wit