DNA contamination is ubiquitous in laboratory reagents commonly used to analyse the microbes that inhabit the human body.
Susannah Salter at the Wellcome Trust Sanger Institute in Hinxton, UK, Alan Walker at the University of Aberdeen, UK, and their colleagues used off-the-shelf DNA-extraction kits and two common techniques to sequence a pure culture of the bacterium Salmonella bongori as well as a series of diluted versions. Contamination by other bacterial species increased with each dilution, and quickly drowned out the original S. bongori signal. The team traced at least part of the problem to the DNA-extraction kits, which are not sold as sterile.
This contamination could undermine microbiome studies, especially in samples that have low microbial content, including those from spinal fluid, blood and the lungs, the authors say.