Table 1. Functional classification of gut microbiota.

	Beneficial bacteria	Neutral bacteria (conditional pathogenic bacteria)	Harmful bacteria
	Bifidobacterium	Escherichia coli	Staphylococcus sp.
	Lactobacillus beijerinck	Candida albicans	Shigella castellani
	Enterococcus	Enterococcus mundtii	Clostridium perfringen
	Akkermanisa	Bacteroides vulgatus	Pseudomonas aeruginosa
	Coprococcus	Actinomycetes	Salmonella minnesota
	Ruminococcus
	Lactobacillus
	Bifidobacterium
	Butyric acid bacteria
	Pectinolytic bacteria
	Enterococcus
	Pseudomonas aeruginosa
Role	Can promote intestinal peristalsis, excrete harmful substances, and prevent pathogen invasion.	Beneficial to health under normal circumstances. Nevertheless, once proliferation is out of control, they will be invasive and harmful to the human body.	May produce harmful substances. It can increase the reabsorption of harmful substances in the intestinal tract, resulting in slow intestinal peristalsis and vulnerability to pathogenic bacteria.