Collection media and delayed freezing effects on microbial composition of human stool.
BACKGROUND
Different bacteria in stool have markedly varied growth and survival when stored at ambient temperature. It is paramount to develop optimal biostabilization of stool samples during collection and assess long-term storage for clinical specimens and epidemiological microbiome studies. We evaluated the effect of collection media and delayed freezing up to 7 days on microbial composition. Ten participants collected triplicate stool samples each into no media as well as RNAlater® with and without kanamycin or ciprofloxacin. For each set of conditions, triplicate samples were frozen on dry ice immediately (time = 0) or frozen at -80 °C after 3-days and 7-days incubation at 25 °C. Microbiota metrics were estimated from Illumina MiSeq sequences of 16S rRNA gene fragments (V3-V4 region). Intraclass correlation coefficients (ICC) across triplicates, collection media, and incubation time were estimated for taxonomy and alpha and beta diversity metrics.


RESULTS
RNAlater® alone yielded the highest ICCs for diversity metrics at time = 0 [ICC median 0.935 (range 0.89-0.97)], but ICCs varied greatly (range 0.44-1.0) for taxa with relative abundances <1%. The 3- and 7-day freezing delays were generally associated with stable beta diversity for all three media conditions. Freezing delay caused increased variance for Shannon index (median ICC 0.77) and especially for observed species abundance (median ICC 0.47). Variance in observed species abundance and in phylogenetic distance whole tree was similarly increased with a 7-day delay. Antibiotics did not mitigate variance. No media had inferior ICCs at time 0 and differed markedly from any media in microbiome composition (e.g., P =0.01 for relative abundance of Bacteroidetes).


CONCLUSIONS
Bacterial community composition was stable for 7 days at room temperature in RNAlater® alone. RNAlater® provides some stability for beta diversity analyses, but analyses of rare taxa will be inaccurate if specimens are not frozen immediately. RNAlater® could be used as collection media with minimal change in the microbiota composition.
Nutritional Science Research Group, Division of Cancer Prevention, National Cancer Institute, National Institutes of Health, 9609 Medical Center Dr. RM5E554-MSC9788, Bethesda, MD 20892 USA.
Roberto
R
Flores
Biostatistics Branch, Division of Cancer Epidemiology and Genetics, NCI/NIH, Bethesda, MD USA.
Jianxin
J
Shi
Infections and Immunoepidemiology Branch DCEG/NCI/NIH, Bethesda, MD USA.
Guoqin
G
Yu
Institute of Genome Sciences, University of Maryland School of Medicine, Baltimore, MD USA.
Bing
B
Ma
Institute of Genome Sciences, University of Maryland School of Medicine, Baltimore, MD USA.
Jacques
J
Ravel
Infections and Immunoepidemiology Branch DCEG/NCI/NIH, Bethesda, MD USA.
James J
JJ
Goedert
Nutritional Epidemiology Branch, DCEG/NCI/NIH, Bethesda, MD USA.
Rashmi
R
Sinha
D001419:Bacteria / Q000145:classification / Q000235:genetics; D044822:Biodiversity; D005243:Feces / Q000382:microbiology*; D005260:Female; D005615:Freezing; D006801:Humans; D008297:Male; D054892:Metagenome; D064307:Microbiota; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D013048:Specimen Handling / Q000379:methods
D012336:RNA, Ribosomal, 16S