Recent advances in microbiome sequencing have rendered new insights into the role of the microbiome in human health with potential clinical implications. Unfortunately, the presence of host DNA in tissue isolates has hampered the analysis of host‐associated bacteria. Here, we present a DNA isolation protocol for tissue, optimized on biopsies from resected human colons (~2–5 mm in size), which includes reduction of human DNA without distortion of relative bacterial abundance at the phylum level. We evaluated which concentrations of Triton and saponin lyse human cells and leave bacterial cells intact, in combination with DNAse treatment to deplete released human DNA. Saponin at a concentration of 0.0125% in PBS lysed host cells, resulting in a 4.5‐fold enrichment of bacterial DNA while preserving the relative abundance of Firmicutes, Bacteroidetes, γ‐Proteobacteria, and Actinobacteria assessed by qPCR. Our optimized protocol was validated in the setting of two large clinical studies on 521 in vivo acquired colon biopsies of 226 patients using shotgun metagenomics. The resulting bacterial profiles exhibited alpha and beta diversities that are similar to the diversities found by 16S rRNA amplicon sequencing. A direct comparison between shotgun metagenomics and 16S rRNA amplicon sequencing of 15 forceps tissue biopsies showed similar bacterial profiles and a similar Shannon diversity index between the sequencing methods. Hereby, we present the first protocol for enriching bacterial DNA from tissue biopsies that allows efficient isolation of all bacteria. Our protocol facilitates analysis of a wide spectrum of bacteria of clinical tissue samples improving their applicability for microbiome research.
Recent advances in microbiome sequencing have rendered new insights into the role of the microbiome in human health with potential clinical implications. Unfortunately, developments in the field of tissue microbiomes have been hampered by the presence of host DNA in isolates which interferes with the analysis of the bacterial content. Here, we present a DNA isolation protocol from tissue samples including reduction of host DNA without distortion of microbial abundance profiles. We evaluated which concentrations of Triton and saponin lyse host cells and leave bacterial cells intact, which was combined with DNAse treatment to deplete released host DNA. We applied our protocol to extract microbial DNA from ex vivo and in vivo acquired human colon biopsies (∼2-5 mm in size) and assessed the relative abundance of bacterial and human DNA by qPCR. Saponin at a concentration of 0.0125% in PBS lysed host cells, resulting in a 4.5-fold enrichment of bacterial DNA while preserving the relative abundance of Firmicutes, Bacteroidetes, γ-Proteobacteria and Actinobacteria. Our protocol combined with shotgun metagenomic sequencing revealed a colon tissue microbiome profile with a Shannon diversity index of 3.2 and an UniFrac distance of 0.54, which is comparable to reported numbers based on amplicon sequencing. Hereby, we present the first protocol for enriching bacterial DNA from tissue biopsies that allows efficient isolation of rigid Gram-positive bacteria without depleting the more sensitive Gram-negative bacteria. Our protocol facilitates analysis of a wide spectrum of bacteria of clinical tissue samples improving their applicability for microbiome research.
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