Analysis of the fecal microflora of human subjects consuming a probiotic product containing Lactobacillus rhamnosus DR20

The composition of the fecal microflora of 10 healthy subjects was monitore d before (6-month control period), during (6-month test period), and after (3-month posttest period) the administration of a milk product containing L actobacillus rhamnosus DR20 (daily dose, 1.6 x 10(9) lactobacilli). Monthly fecal samples were examined by a variety of methods, including bacteriolog ical culture analysis, fluorescent in situ hybridization with group-specifi c DNA probes, denaturing gradient gel electrophoresis of the V2-V3 region o f 16S rRNA genes amplified by PCR, gas-liquid chromatography, and bacterial enzyme activity analysis. The composition of the Lactobacillus population of each subject was analyzed by pulsed-field gel electrophoresis of bacteri al DNA digests in order to differentiate between DR20 and other strains pre sent in the samples. Representative isolates of lactobacilli were identifie d to the species level by sequencing the V2-V3 region of their 16S rRNA gen es and comparing the sequences obtained (BLAST search) to sequences in the GenBank database, DR20 was detected in the feces of all of the subjects dur ing the test period, but at different frequencies, The presence of DR20 amo ng the numerically predominant strains was related to the presence or absen ce of a stable indigenous population of lactobacilli during the control per iod. Strain DR20 did not persist at levels of > 10(2) cells per g in the fe ces of most of the subjects after consumption of the product ceased; the on ly exception was one subject in which this strain was detected for 2 months during the posttest period. We concluded that consumption of the DR20-cont aining milk product transiently altered the Lactobacillus and enterococcal contents of the feces of the majority of consumers without markedly affecti ng biochemical or other bacteriological factors.