Fusobacterium prausnitzii and related species represent a dominant group within the human fecal flora

The human gut microflora plays a key role in nutrition and health. It has b een extensively studied by conventional culture techniques. However these m ethods are difficult, time consuming and their results not always consisten t. Furthermore microscopic counts indicate that only 20 to 40% of the total flora can be cultivated. Among the predominant species of the human gut, F usobacterium prausnitzii was reported either as one of the most frequent an d numerous species or was seldom retrieved. We designed and validated a spe cific rRNA-targeted oligonucleotide probe, called S-*-Fprau-0645-a-A-23, to accurately detect and quantify E prausnitzii and relatives within the huma n fecal microflora. The target group accounted for 5.3 +/- 3% of total bact erial 16S rRNA using dot blot hybridization (10 human fecal samples) and 16 .5 +/- 7% of cells stained with Dapi using in situ hybridization (10 other human fecal samples). A specific morphology seemed to be typical and domina nt: two cells forming an asymmetrical double droplet. This work showed that F. prausnitzii and phylogenetically related species represent a dominant g roup within the human fecal flora.