Normalized N0-values obtained from the same amplicon group, for example phylum Bacteroidetes, are directly comparable to each other and may thus be used to determine the fold-change of specific groups of bacteria between two or more samples. Direct comparisons between different

amplicon groups may, however, be biased due to, for example, differences click here in amplicon length and GC-content causing nonequal binding of SYBR Green. Analysis of the fecal samples obtained from six infants at both 9 and 18 months was performed by PCA of normalized N0-values calculated from GULDA (Fig. 2). The score plot shows that all six individuals migrated from left to right along the PC#1 with Akt inhibitor generally little movement vertically along the PC#2. The initial grouping appeared more confined for the individuals at 9 months as compared to 18 months, which is consistent with the development of a more complex and individual gut microbiota. The loading plot indicates which bacterial taxa drive this migration, which was further studied by calculating the fold-changes for specific

amplicon groups (Fig. 3). The latter shows a significant (P < 0.05) increase in the relative abundance of Clostridial cluster IV (Clostridia leptum group) and Bifidobacterium bifidum and concurrent significant decrease in the abundance of Clostridium butyricum (Clostridial cluster I) and a tendency for decrease in Enterobacteriaceae and E. coli (P < 0.10) from 9 to 18 months of age. These findings are consistent with some of

the results of a previous study using both qPCR and Northern blotting to characterize intestinal bacteria in infant stools (Hopkins et al., 2005), which showed a significant decrease in Enterobacteria and increase in Faecalibacterium prausnitzii (Clostridial cluster IV) rRNA after 6 months of age. No other significant changes were observed within the remaining 26 amplification groups in the present study. Although a fairly small dataset, n = 6 infants, was used in this study, the methodological protocol of calculating the changes in a microbial community over a time period by the use of relative qPCR determinations performed under universal temperature cycling conditions was successfully demonstrated. In the present study, multiple bifidobacterial species IKBKE were included in the array as this genus is known to be highly represented during infancy (Roger et al., 2010). Modification of GULDA for other purposes by incorporating other primer sets is, however, easily achieved and provides a high degree of flexibility to the qPCR array. We expect GULDA to be a very useful tool to study induced changes in the composition of the gut microbiota and consequently further elucidate the causal relationships between the vast numbers of bacterial species present in the human gut microbiota.