Table 3.

Bacterial types, location within the gastrointestinal tract, and function

Bacteria	Location in the GI Tract	Functional Role	Ref.
Lactobacillus	Stomach, duodenum, jejunum, ileum, colon	Improved digestion and absorption of nutrients; inhibition of the growth of pathogens by activating the immune system a,b	[132,133,134]
Streptococcus	Jejunum, ileum, colon	Modulation of the immune system through altered cytokine release from immune cellsc	[135,136]
Bacteroides	Jejunum, ileum, colon	Production of SCFAs involved in energy homeostasis and regulation of intestinal inflammationd	[137]
Bifidobacterium	Jejunum, ileum, colon	Inhibition of the growth of pathogens by activating the immune system; amino-acid and vitamin synthesisd	[138,139]
Veillonella	Colon	Production of SCFAs involved in energy homeostasisc,d	[140]
Eubacteria	Colon	Production of SCFAs involved in energy homeostasis and regulation of intestinal inflammationc	[141]
Clostridia	Colon	Participation in resistance to the colonization of pathogens; production of SCFAsc; maintenance of gut homeostasisc	[142,143,144]
Peptostreptococcus	Colon	Maintenance of epithelial barrier and modulation of intestinal inflammationc,d	[145]

^a Dog; ^b cat; ^c human; ^d rodent.