**2.5 Gestational age at birth**

Due to organ development and external influences such as antibiotics, hospitalization, and enteral feeding, colonization is a concern in preterm neonates after birth [53, 54]. For these reasons, preterm birth might have had a considerable influence on gut and systemic immunity throughout pregnancy [54].

Preterm newborns have a limited range of bacteria, with more potentially hazardous microbes again from the Proteobacteria phylum's Bacteria cell colonizing them [53] and decreased rates of strictly anaerobic bacteria like Bifidobacteria and lactobacilli [55], Bacteroides, and Atopobium [53]. Genetic factors, as well as the family's secretor and Lewis blood type, impact the composition of infant formula, resulting in four phenotypes with varied amounts of oligosaccharide [56]. Premature children born to non-secretor mothers had greater Proteobacteria levels and lower Firmicutes levels [57]. Pratic et al. [58] investigated the makeup of colostrum that discovered that Health maintenance organizations linked with different mother phenotypes

*Obesity and Gut Microbiota DOI: http://dx.doi.org/10.5772/intechopen.105397*

influence the gut microbiota of newborns. For example, health centers associated with secretor moms might provide a prebiotic benefit by lowering microorganisms linked to sepsis and necrotizing enterocolitis [57]. This suggests that health centers can alter gut flora, protecting premature babies against gut dysfunction and NEC [59]. Lactoferrin is a well-known component of human dairy that promotes the colonizing of preterm newborns' stomachs with helpful bacteria, therefore improving their ecology [32].

## **2.6 Type of delivery**

Babies acquire a gut that is identical to their mother's gut microflora after normal delivery. The flora of the child's large intestine and the related organisms of the vaginal tract, Bacteria, Lactobacilli, and Sneathia, were discovered to be closely linked in the development of biological baby mucus [60]. As per Biasucci et al. [61], significant bacteria such as Probiotic bacteria long and Lactobacillus catenulatum are familiar with the microbiome of perineal born neonates. *E. coli*, Staphylococcus, *Bacteroides fragilis*, and Bacteria are among the aerotolerant anaerobic bacteria found inside the infant gut [62–64].

In analyses done at 7 years old, variations in the microflora of C-section and perineal delivered infants were discovered [65]. Persistent autoimmune abnormalities like influenza, regional collagenous disorders, adolescent arthritis, irritable bowel [66], or overweight [67] have been linked to cesarean delivery.

#### **2.7 Methods of milk feeding**

As per research [68, 69], Equation babies are more likely to be contaminated with *E. coli*, Bacteroides, and Clostridium difficult than breastfeeding infants. In terms of Actinobacteria concentration, Bifidobacterium spp. has been connected to breastfeeding and artificial milk [70, 71]. In contrast to equation babies, breastfed infants have a more diverse and variable Probiotic bacteria microbiota [71]. Breastfeeding infants are provided microbiota for a more than 2 increase in Acidophilus cells as compared to supplemented infants [70]. Breastfed babies had a more favorable gut microbiota than pattern babies, with more Bifidobacterium spp. and less *Clostridium difficile* and *Escherichia coli* [23].

Maintaining a healthy and nourishing gut flora in the mother during pregnancy is also regarded to be a crucial factor in improving the milk microbiome composition. Oral supplements may increase the quantity of Acidophilus spp. and Lactobacilli spp. in human breast milk in vaginally delivered mothers [72].

#### **2.8 Weaning period**

When solid foods are introduced and dairy is eliminated, significant changes in gut flora occur. Probiotics, Escherichia coccoides, and Bifidobacteria are the most frequent species after childhood [73]. Apigenin muciniphila, Enterobacteriaceae, Veillonella, Mycobacterium coccoides spp., and Botulism spp. are all found in significant levels in the microbiota of one baby [74]. Around the age of three, the appearance and diversity of a toddler's intestinal microbiota are most akin to those of adults [75]. *Bacillus subtilis*, Bacteroidetes, and Act are the three bacterial phyla that control the adult microbial population.

#### **2.9 Antibiotics**

Pharmaceuticals could alter the intestinal microbiota's makeup to some extent. The influence of antibiotic molecular pathways on the makeup of the human microbiome was investigated in obey research [76], Penicillin treatment options alter the gut microbiota, increasing the prevalence of some species while decreasing the abundance of others. Bacterial diversity and abundance decreased during therapy. Antimicrobial class, frequency, length of therapy, pharmacokinetic properties, and target microorganisms all impact gut flora composition [77]. Antibiotic features such as antimicrobial actions and potency are important in the development of gut flora thus they are partly to blame for bacterial composition changes following antibiotic therapy [76]. The drug has unique properties and disposal methods, resulting in a wide range of bacteria material changes [77].

#### **2.10 Gut microbiota variations between individuals**

We've previously seen how single intestinal microbiota makeup changes, and now we'll examine how it varies among individuals. Intertype's, BMI levels, and extrinsic variables including behavior, health and body, race, and culinary or cultural traditions all impact cross variability.

#### **2.11 Enterotypes**

We've established that the gut flora composition differs across persons; now we'll investigate how it varies between individuals. Exogenous variables including activity regularity, race, culinary and cultural habits, enterotypes, and BMI levels all play a role in these variances. Instead of an intentional integration of germs, an enterotype is a physiologically close relation between distinct species of bacteria. Although enterotypes are not as different from plasma groups in terms of structure, they are tolerant, constant through life, and may be regained if they are changed. Enterotypes appear to be mostly defined by food habits. Knowing the genesis and roles of enterotypes might help researchers better understand the links between gut flora and people's health.

#### **2.12 Body mass index**

Many investigations [78, 79] focused on the impact of childhood obesity on intestinal flora and found that overweight or medium BMI kids had more bacterial ecology than underweight students. Intestinal flora declines with time, depending on the BMI category [78, 80]. Obese children's microbiota has a greater Firmicutesto-Bacteroidetes ratio than lean children's microbiota, according to Bervoets et al. [81]. On the other hand, this obese microbiome exhibits comparably low percentages of Probiotic bacteria vulgatus and high levels of Escherichia species [81]. Adiposity is also linked to higher levels of Genus like Ruminococcaceae and decreased rates of Clostridium such as Bacteroidaceae and Enterobacter, according to Riva et al. [82]. Short-chain fatty acids were found to be higher in obese children, indicating that they used more fuel. Increased SCFA production and energy extraction from colon digestion are connected to a higher Firmicutes to Bacteroidetes ratio, indicating that intestinal flora imbalance might play a role in obesity etiology [82]. Gut flora instability is well predicted by BMI.
