Ne at day 8 (10.960.1 log10) (Fig. 1). All fecal samples contained bifidobacterial 16S rRNA gene copies ranging from 4.8 to 11.2 log10. Before AMC exposure, only two subjects had bifidobacterial counts #6.2 log10 copies/g and showed low counts after. Six subjects had marked decrease of bifidobacterial number at day 5 and the 10 other subjects showed no significant quantitative change at the same period. Mean 16S rRNA gene copy numbers of bifidobacteria 18325633 per gram of feces were 9.460.3 log10 before AMC exposure and 8.160.5 log10 (p = 0.003) at day 5. In percentages of total bacteria, there was no significant difference at day 5 (7.462.6 vs 12.662.6 at day 0). Total bifidobacteria 16S rRNA gene copy numbers also returned to baseline at day 8 (9.160.5 log10 copies/g).Impact of antibiotic therapy on bifidobacterial microbiotaThe bifidobacterial TTGE profiles were composed of 1 to 7 bands. Only one subject failed to present TTGE profiles due to a weak cell amount (about 4.8 log10). Three types of TTGE profile evolutions were observed over time: some microbiota did not change BIBS39 chemical information during the whole study (n = 3), a few showed a return to baseline after being changed by antibiotics (n = 5) (Fig. 4A), and for the others, the species balance perturbed at day 5 did not return toFigure 1. Monitoring of total bacteria and bifidobacterial counts using qPCR before and after AMC exposure (day0 ay5). doi:10.1371/journal.pone.0050257.gBifidobacterium Monitoring after AMC ExposureFigure 2. Mean similarity coefficients of TTGE profiles of samples collected before and after AMC exposure (day0 ay5) and calculated according to the reference period (day-12 day-6 day 0; n = 18). doi:10.1371/journal.pone.0050257.gFigure 3. TTGE profiles representing the bacterial diversity of fecal samples from two healthy volunteers (A and B) before and after AMC exposure. 1: day-12; 2: day-6; 3: day 0; 4: day 5; 5: day 8; 6: day 12; 7: day 19; 8: day 26; 9: day 33; 10: day 64. doi:10.1371/journal.pone.0050257.gBifidobacterium Monitoring after AMC Exposurebaseline at day 33 nor at day 64 (n = 9) (Fig. 4B). The intraindividual similarity indices of the TTGE profiles were calculated, considering day -12, -6 and 0 as reference period. Mean similarity percentage within reference period was 84.5 64.1 . Only seven subjects presented a 100 similarity between day-12, day-6 and day 0, but twelve subjects presented a 100 similarity between day -6 and day 0 and little variations occurred for the others. At day 5, mean similarity percentages were 55.8 67.6 . The microbiota of three subjects did not respond to AMC BI-78D3 site treatment (Dice’s similarity coefficient 100 at day 5 and day 8), whereas there was a marked change of TTGE profiles for the others. One or two months after the end of AMC treatment, the mean similarity percentages of TTGE profiles 
were 59.6 and 62.3 respectively, showing that microbiota was still modified. To improve comparisons, two groups were constituted. The first gathered 
volunteers with Dice’s similarity coefficients at day 64 80 (corresponding to the mean observed during reference period (n = 5)) and the others (n = 12) (Fig. 5). The microbiota of three individuals within the 5 showed marked alterations of TTGE profiles at day 5 (or day 8) and returned to similarity percentages 90 at day 64. The last two microbiota were resistant to AMC. In this group, the microbiota studied in the reference period was very stable (100 similarity). Among the other volunteers microbiota.Ne at day 8 (10.960.1 log10) (Fig. 1). All fecal samples contained bifidobacterial 16S rRNA gene copies ranging from 4.8 to 11.2 log10. Before AMC exposure, only two subjects had bifidobacterial counts #6.2 log10 copies/g and showed low counts after. Six subjects had marked decrease of bifidobacterial number at day 5 and the 10 other subjects showed no significant quantitative change at the same period. Mean 16S rRNA gene copy numbers of bifidobacteria 18325633 per gram of feces were 9.460.3 log10 before AMC exposure and 8.160.5 log10 (p = 0.003) at day 5. In percentages of total bacteria, there was no significant difference at day 5 (7.462.6 vs 12.662.6 at day 0). Total bifidobacteria 16S rRNA gene copy numbers also returned to baseline at day 8 (9.160.5 log10 copies/g).Impact of antibiotic therapy on bifidobacterial microbiotaThe bifidobacterial TTGE profiles were composed of 1 to 7 bands. Only one subject failed to present TTGE profiles due to a weak cell amount (about 4.8 log10). Three types of TTGE profile evolutions were observed over time: some microbiota did not change during the whole study (n = 3), a few showed a return to baseline after being changed by antibiotics (n = 5) (Fig. 4A), and for the others, the species balance perturbed at day 5 did not return toFigure 1. Monitoring of total bacteria and bifidobacterial counts using qPCR before and after AMC exposure (day0 ay5). doi:10.1371/journal.pone.0050257.gBifidobacterium Monitoring after AMC ExposureFigure 2. Mean similarity coefficients of TTGE profiles of samples collected before and after AMC exposure (day0 ay5) and calculated according to the reference period (day-12 day-6 day 0; n = 18). doi:10.1371/journal.pone.0050257.gFigure 3. TTGE profiles representing the bacterial diversity of fecal samples from two healthy volunteers (A and B) before and after AMC exposure. 1: day-12; 2: day-6; 3: day 0; 4: day 5; 5: day 8; 6: day 12; 7: day 19; 8: day 26; 9: day 33; 10: day 64. doi:10.1371/journal.pone.0050257.gBifidobacterium Monitoring after AMC Exposurebaseline at day 33 nor at day 64 (n = 9) (Fig. 4B). The intraindividual similarity indices of the TTGE profiles were calculated, considering day -12, -6 and 0 as reference period. Mean similarity percentage within reference period was 84.5 64.1 . Only seven subjects presented a 100 similarity between day-12, day-6 and day 0, but twelve subjects presented a 100 similarity between day -6 and day 0 and little variations occurred for the others. At day 5, mean similarity percentages were 55.8 67.6 . The microbiota of three subjects did not respond to AMC treatment (Dice’s similarity coefficient 100 at day 5 and day 8), whereas there was a marked change of TTGE profiles for the others. One or two months after the end of AMC treatment, the mean similarity percentages of TTGE profiles were 59.6 and 62.3 respectively, showing that microbiota was still modified. To improve comparisons, two groups were constituted. The first gathered volunteers with Dice’s similarity coefficients at day 64 80 (corresponding to the mean observed during reference period (n = 5)) and the others (n = 12) (Fig. 5). The microbiota of three individuals within the 5 showed marked alterations of TTGE profiles at day 5 (or day 8) and returned to similarity percentages 90 at day 64. The last two microbiota were resistant to AMC. In this group, the microbiota studied in the reference period was very stable (100 similarity). Among the other volunteers microbiota.