Another important factor that influences NGS-related microbiota profiling is competition between different 16S rRNA molecules, resulting in unequal/preferential amplification rates for certain amplicon sequences. The result of competition can be an over- or underestimation of particular OTUs. For example, in our current experiments we utilized a synthetic community consisting of 20 bacterial species that are each present at an equimolar concentration of 5% of 16 S rRNA genes. MicPCR/NGS data showed an average 0.85-fold difference from the 5% OTU frequency expected in the synthetic community, with a maximum overestimation of 1.73-fold for Listeria monocytogenes and a maximum underestimation of 0.28-fold for Streptococcus pneumoniae (Fig. 2). In contrast, the OTU differences associated with PCR competition and traditional PCR/NGS were more extreme, yielding an average 0.65-fold difference in OTU frequency above the expected frequency, with an overestimated maximum of 2.31-fold for Bacteriodes vulgatus and an underestimated maximum of 0.04-fold for Helicobacter pylori. These findings are in agreement with the previously reported consistent overestimation of Bacteriodes spp. and underestimation of Helicobacter spp. in four different laboratories when investigating an identical synthetic communit