TABLE 2.

Summary of OTU selected by each method.

	Saliva	Stool	Total number
Total OTU number	381	405	548
Total Read count	331,977	267,234	599,211
	Young	Old	Young	Old
Age-associated OTU	120	35	39	150
Age-associated reads	20,038	21,189	60,876	26,232
Binary OTU	103	27	24	131
Binary reads	3,105	219	1,657	11,866
LEfSe	29	2	13	24
LEfSe reads	16,331	16,627	60,262	10,584
Random Forest (RF)	23	7	12	18
RF reads	7,513	5,120	7,926	8,806

Operational taxonomic unit (OTU) was calculated using a de novo OTU picking protocol with a 95% similarity threshold.