Not all probiotics are the same: A closer look at probiotics and its roles in the management of diarrhea

Development of gut microbiota
Human fertilization occurs in the uterus, an immune-protected organ,where there is lack of bacterial colonization.The mode of delivery affects the development of the gut microbiota as it closely resembles the microbiota it encountered during birth. In infants delivered vaginally, the gut microbiota is dominated by Lactobacillus, Prevotella or Sneathia; in infants born by caesarean section, the gut microbiota is similar to skin microbiota, which is dominated by Staphylococcus, Corynebacterium and Propionibacterium. [Gut 2019;68:1108–1114; Allergol Int 2017;66:515–522]

Figure 1 shows that an infant’s gut microbiota is established after birth and it generally accompanies two big transitions:The first occurs during lactation while the second occurs during the weaning period with the introduction of solid foods. These alterations continue until the child is 3 years of age, during which there is a selection for bacterial population with relevant metabolic activities and the microbial diversity of the intestine increases steadily. Each person has a unique microbiota and over time, even the same person can have a different microbiota compared with their own prior representation. [Gut 2019;68:1108–1114; Allergol Int 2017;66:515–522]

The intestinal colonization affects the development and physiology of the host immune system in early life and subsequently, affects its health later in life. Moreover, functional redundancy makes the characterization of the healthy microbiome extremely complex. [Gut 2019;68:1108–1114; Allergol Int 2017;66:515–522]