Microbial profiling is feasible using both long-term frozen and buffered fecal samples. FIT_NORCCAP_Fresh_pilot

Associations between colorectal cancer and microbiota have been identified. Thus, there is a need for exploration of host-microbiota interactions and causality in carcinogenesis and development of microbial biomarkers for cancer prevention. The fecal samples used in fecal occult blood tests from screening participants worldwide might be a valuable source in microbial biomarkers discovery or longitudinal studies. However, the quality, quantity and stability of the microbiota in these fecal samples must be assessed prior to such studies. We compared the fecal microbiota in long-term stored samples, buffered samples used for fecal immunochemical tests and fresh samples. We also tested fresh, directly frozen vs. fresh samples stored at room temperature at 48 hours. The microbiota profiles were obtained by sequencing the V3-V4 region of 16S rDNA gene. The fecal immunochemical test do not introduce cross sample contamination detectable by qPCR. Microbial profiling was successful in 100 % of fresh, 81% of long-term frozen (archived) and 96% of buffered samples. Microbial richness and composition were comparable between fresh and buffered samples, but differed significantly between long-term frozen and buffered samples. We showed high stability of the fecal microbiota in samples exposed to room temperature for 48 hours, compared to directly frozen samples. Our data showed that it is feasible to exploit the large fecal sample sets, high quality diagnostic and follow-up data from colorectal cancer screening for the purpose of microbial biomarker discovery and longitudinal observational studies. However, care must be taken when the microbiota are profiled in long-term stored fecal samples.