Bibliometric analysis of subject trends and knowledge structures of gut microbiota

Table 2 Results of biclustering analysis on high-frequency major Medical Subject Heading terms/Medical Subject Heading subheadings in the research field of gut microbiota in three periods

Period	Cluster	Number of MeSH terms1	Cluster analysis
2004-2008	0	1, 8, 12, 15, 19, 23, 31, 46	(1) Intestinal mucosa and intestines metabolism; and (2) Probiotics pharmacology.
	1	6, 7, 13, 17, 22, 28, 34, 36, 44	(1) Inflammatory bowel diseases microbiology and immunology; (2) Gut microbiota immunology; and (3) Intestinal mucosa immunology and microbiology.
	2	5, 9, 20, 25, 26, 29, 35, 39, 40, 41, 48	(1) Bifidobacterium metabolism, physiology and drug effects; and (2) Bifidobacterium growth and development.
	3	2, 10, 16, 21, 27, 32, 33, 38, 42, 49	(1) Inflammatory bowel disease drug therapy; and (2) Probiotics therapeutic use.
	4	3, 4, 11, 14, 18, 24, 30, 37, 43, 45, 47, 50	(1) Feces microbiology and gastrointestinal tract microbiology; (2) Gut microbiota isolation, purification classification, growth and development; and (3) Irritable bowel syndrome microbiology.
2009-2013	0	8, 17, 21, 25, 26, 29, 31, 34, 35	(1) Gastrointestinal tract immunology; (2) Inflammatory bowel diseases microbiology and immunology; and (3) Intestinal mucosa microbiology and immunology.
	1	10, 20, 23, 30, 33, 39, 42, 44	(1) Anti-bacterial agents pharmacology, therapeutic use and adverse effects; and (2) Gut microbiota growth and development.
	2	3, 4, 14, 15, 18, 19, 22, 28, 32, 38, 40, 43	(1) Irritable bowel syndrome microbiology; (2) Gut microbiota classification, isolation and purification; and (3) Feces microbiology.
	3	1, 2, 5, 6, 7, 9, 11, 12, 13, 16, 24, 27, 36, 37, 41	(1) Intestines and intestinal mucosa metabolism; (2) Gastrointestinal tract microbiology; (3) Obesity microbiology; and (4) Probiotics pharmacology and therapeutic use.
2014-2018	0	7, 9, 15, 17, 27, 28, 31, 46, 55, 65	(1) Gut microbiota genetics; (2) Metagenomics methods; and (3) Feces microbiology.
	1	8, 23, 30, 32, 38, 40, 57, 58, 59, 60, 66	(1) Inflammatory bowel diseases immunology; (2) Fecal microbiota transplantation methods; (3) Gastrointestinal tract and intestinal mucosa immunology; and (4) Intestinal mucosa immunology.
	2	18, 20, 21, 29, 34, 42, 44, 53, 54, 56	(1) Irritable bowel syndrome microbiology; (2) Dysbiosis microbiology; (3) Gut microbiota growth and development; and (4) Intestinal mucosa microbiology.
	3	1, 4, 5, 10, 11, 14, 19, 25, 45, 51, 61	(1) Probiotics therapeutic use; and (2) Intestines and intestinal mucosa metabolism.
	4	6, 13, 22, 24, 26, 35, 37, 41, 47, 48, 62, 63	(1) Anti-bacterial agents pharmacology, therapeutic use and adverse effects; and (2) Prebiotics therapeutic use and pharmacology.
	5	2, 3, 12, 16, 33, 36, 39, 43, 49, 50, 52, 64	(1) Gastrointestinal tract microbiology; and (2) Non-alcoholic fatty liver disease, obesity and diabetes mellitus (type2) microbiology.

¹Represents the serial number of high-frequency major Medical Subject Heading (MeSH) terms/MeSH subheadings in each period which shown in Supplementary Tables 5-7.