Figure 1.

Microbiota load and diversity vary throughout the gastrointestinal tract. In a healthy individual, the microbiota count, measured as colony-forming units (cfu)/mL, in the human gastrointestinal tract increases from the stomach/duodenum to the jejunum/ileum to the colon. Additionally, the regional diversity in the gastrointestinal microbiome, known as the microbial landscape, increases from the mouth (rostral) to the anus (caudal). Importantly, there is significant intra- and interpersonal variation in the composition of the human microbiome, which is further influenced by various factors such as the mode of infant delivery and feeding, aging, diet composition, geography, medication, stress, and many others [13].