Lifestyle Diseases in Adolescents: Diseases, Disorders, and Preventive Measures

Microbiome in Teenagers – Acquisition and Development

Pallabi Chatterjee¹, *, Isra Aman Aziz², Amarjit Singh³, Aditi Singh²

¹ School of Health Sciences and Technology, University of Petroleum and Energy Studies (UPES), Dehradun, India

² Amity Institute of Biotechnology, Amity University Uttar Pradesh Lucknow Campus, Lucknow-226028, India

³ Department of Centre for Medical Biotechnology, Maharshi Dayanand University, Rohtak, Haryana, India

Abstract

Adolescence is the stage of life between childhood and adulthood, ranging from 10 to 19 years. It is a distinct period in human development and crucial for setting the groundwork for long-term health. Teenagers grow quickly in terms of their physical, cognitive, and emotional development.In the body of teenagers, major changes in microorganisms take place. With the development of these changes in the microbiome of teenagers, diseases are also developed. Teenagers are the future of the world. Microbiota and diseases have an impact on their emotions, thoughts, decisions, and interactions with others and their environment. This chapter is written to acknowledge the readers about the resident microorganisms of the human body during adolescence and the many kinds of changes that occur in the microbiome due to lifestyle changes.

Keywords: Adolescence, Microorganisms, Microbial diseases.

* Corresponding author Pallabi Chatterjee: School of Health Sciences and Technology, University of Petroleum and Energy Studies (UPES), Dehradun, India, Tel: +91 7980175343; E-mail: [email protected]

1. INTRODUCTION

The human microbiome is a vast and complex community of microorganisms, including bacteria, archaea, fungi, and viruses, that reside on and within our bodies. These tiny organisms outnumber human cells by 10 to 1 and play a crucial role in our health and well-being. Microbes inhabit various body sites, including the gut, skin, mouth, and respiratory tract. Each site has a unique microbiome composition adapted to its specific environment (Dekaboruah et al., 2020). The microbiome performs diverse functions, including aiding in digestion and nutrient absorption, regulating the immune system, protecting against pathogens, and even

influencing mood and behavior. A balanced and diverse microbiome is associated with good health, while disruptions can contribute to various diseases, such as obesity, inflammatory bowel disease, and allergies. Diet, lifestyle, medications, and even age can all influence the composition and function of the microbiome. Studying the human microbiome is a rapidly growing field with the potential to revolutionize our understanding of health and disease. By understanding and nurturing our microbiome, we may be able to improve our overall health and well-being in profound ways. The teenage microbiome is a dynamic and evolving ecosystem undergoing significant changes during puberty due to hormonal shifts, dietary habits, and lifestyle factors (Yue and Zhang, 2024). Here is a glimpse into the unique characteristics of a teenager's microbiome:

Shifting composition: Compared to childhood, the gut microbiome in adolescence exhibits a decrease in beneficial bacteria like Bifidobacteria and an increase in Firmicutes, which can influence metabolism and weight regulation.

Impact of diet: Teenage dietary choices significantly impact the gut microbiome. A diet rich in fruits, vegetables, and whole grains promotes a diverse and healthy microbiome, while sugary and processed foods can contribute to harmful bacterial overgrowth.

Stress and the microbiome: The teenage years are often marked by increased stress, which can disrupt the gut microbiome and contribute to digestive issues and inflammation.

The gut-brain connection: The gut microbiome plays a crucial role in brain development and function during adolescence. Studies suggest that a healthy microbiome may positively impact mood, cognitive function, and mental well-being.

2. THE NORMAL MICROBIOME OF ADOLESCENCE

The microbes that live on body surfaces protected by epithelial cells are considered to be members of the normal microbiome. They are found in the systems that are exposed to the outside environment, such as the gastrointestinal tract, respiratory system, vagina, and skin. More bacteria may be present on mucosal and skin surfaces than human cells (Tannock, 1999). The average human body has roughly 10¹³ cells and about 10¹⁴ bacteria (Davis, 1996). Commensal bacteria evolve together with their hosts, but under some circumstances, they are able to get past the host's defenses and cause pathology. Local bacteria create intricate ecosystems with a huge diversity. The distal portions of the gut contain the largest microbiome, and a great deal of the microbes in the gut are gram-negative anaerobes (Pasparakis et al., 2014). Conventional microbiological methods are unable to cultivate more than 50% of gut bacteria. Numerous elements of the local microbiome are capable of triggering both innate and adaptive immunity. Every individual has a diverse microbial flora on their skin and mucous membranes from soon after birth until death (Davis, 1996; Naik et al., 2012). The typical microbial flora is made up of this particular bacterial population. The typical microbial flora is rather constant, with distinct genera inhabiting different bodily locations at different times of a person's life (Fyhrquist et al., 2014). In spite of the fact that the majority of the typical microbial flora that lives in the human skin, nails, eyes, oropharynx, genitalia, and gastrointestinal system is harmless in healthy people, these organisms commonly cause illness in weak hosts. Most researchers do not consider viruses and parasites to be part of typical microbial fauna since they are not considered commensal and do not benefit the host (Palm et al., 2015).

2.1. Resident Flora

They consist of relatively fixed types of microorganisms regularly found in each area at a particular age (Fig. 1). If disturbed, it promptly re-establishes itself.

If the resident flora is disturbed, transient microorganisms may colonize, proliferate and produce disease.

Regularly present in a particular part of the body

They prevent or suppress the colonization or invasion of the body by other pathogens.

They produce antibodies and raise the immune status of the body against pathogens having related antigens.

These microorganisms become opportunistic pathogens and cause clinical disease when they enter a different habitat.

Fig. (1))

Resident flora vs. transient flora.

2.2. Transient Flora

They consist of nonpathogenic or potent pathogenic microorganisms that inhabit the shin or mucous membrane for hours, days or weeks. It is derived from the environment, does not produce disease and does not establish itself permanently on the surface (Fig. 1).

3. The Skin

The teenage skin constantly receives microorganisms from the air and objects with which it comes in contact with, but most of them do not grow on the skin because of the absence of suitable growth conditions and due to the presence of bactericidal substances. The skin of youth contains rich resident flora (10²-10⁴ vi per cm²). The diversity of skin microbiota at age 14 is quite similar to that seen in adults. Furthermore, the youngest and oldest age groups often have the highest skin microbial composition integrity (Sanford et al., 2013).

Transient microbiomes that tend to occur more frequently on the skin are anaerobic Diphtheroid, Actinobacteria spp, Propionibacterium spp, Corynebacterium spp, Lactobacillus spp, Micrococci spp, Streptococcus spp, Escherichia coli, Proteus spp, etc. (Schanche et al., 2015).

Moist skin supports a more prolific flora than dry skin. Humidity, occupational exposure and clothing also influence its character (Ruokolainen et al., 2015).

The relatively dry surface of the skin is inhibitory to microbial growth. When allowed to dry, many bacteria enter a dormant condition (Lehtimäki et al., 2017).

4. Mouth and Respiratory Tract

The mucous membranes of the mouth and pharynx are often sterile at birth, but maybe contaminated by passage through the birth canal (Mummolo et al., 2018). Within 4-12 hours after birth, Viridans streptococci become established as the most predominant members of the resident flora and remain so for life. In the pharynx and trachea, a similar flora establishes itself, whereas few bacteria are found in normal bronchi. Small bronchi and alveoli are normally sterile (Konno et al., 2006).

4.1. Nose

The predominant Corynebacteria spp, Streptococci spp and Staphylococci (S. epidermidis, S. aureus) are found in the nose's flora.

4.2. Mouth and the Pharynx

The mucous membranes of the mouth and pharynx are frequently sterile at birth, but they might become infected after delivery. Viridans streptococci establish themselves 4 to 12 hours after birth, being the dominant members of the local flava (Oishi et al., 2021).

Early in life, gram-negative diplococci (Neisseriae, Moraxella catarrhalis), aerobic and anaerobic Staphylococci, Diphtheroid, and occasional Lactobacilli are introduced.

Corynebacteria spp, Staphylococci (S. epidermidis, S. aureus), Streptococci (S. mutans, S. mitis, S. oralis, S. salivarius, S. pneumonaie, S. pyogenes, etc.), and Haemophilus spp. are some resident microorganisms of mouth (Robinson et al., 2004).

4.3. Teeth

Anaerobic spirochetes are bacteria present in the oral cavity. Along with some naturally existing anaerobic Vibrios and Lactobacilli spp., Fusobacterium spp., Rothia spp., andCapnocytophaga spp. establish themselves. In the mouth, yeast (Candida spp.) can be found.

4.4. Upper and Lower Respiratory Systems

• Similar flora develops in the pharynx and trachea, although few bacteria are present in normal bronchi. Alveoli and tiny bronchi are common features.

• The predominant microorganisms in the upper respiratory tract, particularly the pharynx, are nonhemolytic and alpha homolytic Streptococci and Neisserice spp.

• Additionally encountered are Staphylococci, Diphtheroid, Haemophile, Pneumococa, Mycoplasmas, and Prevotellae spp. (Kumpitsch et al., 2019)

• Lower airways, bronchioles, and the trachea are typical. To rule out simple colonization, penetration of the microorganisms into tissue must be proven. Sterile fungi, including C. albicans, are an uncommon cause of illness in the lower airway (Pulvirenti et al., 2019).

5. Gastrointestinal Tract

The gut microbiota (Fig. 2) of an adolescent is essential for many fundamental elements of health, and maintaining host fitness throughout youth and later in life depends on its appropriate growth from a young age. While going through adolescence, a time of significant physical, hormonal, mental, and social changes, microbial community transition processes continue.

Fig. (2))

The predominant types of intestinal microflora. The population is most numerous in the ileum and colon.

5.1. Stomach

Along with food and water, the stomach receives a huge number of microorganisms from the mouth, but the antibacterial action of HCl destroys most of them (Tennant et al., 2008). Few bacteria that can withstand stomach acidity can create the stomach's usual resident flora. Streptococcus, Staphylococcus, Lactobacillus, and Peptostreptococcus are the primary bacteria that live in the stomach. A gram-negative spiral bacteria called Helicobacter pylori attaches to the stomach mucosa and causes chronic gastritis and peptic ulcer disease, and is a known carcinogen for gastric cancer.

5.2. Small Intestine

• The jejunum connects the duodenum and ilium, the two segments that make up the small intestine.

• The bulk of the bacteria found in the duodenum, which is located next to the stomach and is somewhat acidic, are gram-positive cocci and bacilli. The duodenum and stomach are similar in that they lack a microbial ecology (Hollister et al., 2015).

• The jejunum is the second segment of the small intestine. Occasionally, different enterococci species are discovered, likeMycobacterium species, Clostridium species, and Lactobacilli and Diphtheroid (Rothschild et al., 2018).

• The pH increases progressively from the duodenum to the ileum. The ileum, the distal end of the small intestine, is less acidic, and more microorganisms are present there. Here, anaerobic bacteria, including members of the family Enterobacteriaceae, flourish and are numerous (Zhong et al., 2019).

5.3. Large Intestine

• The first part of the large intestine, the cecum, receives the contents of the ileum. The remainder of the big colon is made up of the colon on the large intestine, which houses the majority of the human body's bacteria.

• According to estimates, there are around 10¹³ bacteria per gram of moist weight in stool samples. The large intestine's normal flora is primarily strictly anaerobic, with some facultatively or aerotolerant.

• Mandatory anaerobic bacteria Bacteroides fragilis, Bacteroides oralis, and Bacteroides melaninogenicus are the main gram-negative bacteroid species. Other obligatory anaerobes include Peptococcus spp., Ruminococcus spp., and Fusobacterium spp. (Cheng et al., 2015).

• Gram-positive bacteria includeClostridium spp., Coprococcus spp. Bifidobacterium bifidum species, Lactobacilli species, and Eubacterium libosum (Hollister et al., 2015).

• There are fewer facultative anaerobes to be discovered. Examples include Klebsiella pneumoniae, Proteus spp, Escherichia coli, and Streptococcus faecalis.

• Additionally, the Yeast Candida albicans is present (Ringel-Kulka et al., 2013).

• In the gut, where they develop, certain protozoa may also be present as commensals. Anaerobically, by consuming the local microorganisms, a flagellated protozoon, for instance, Trichomonas hominis, resides in the cecum region of the gastrointestinal system. Another illustration is the fact that the colon is home to a variety of amoeba from the genera Indamoeba spp., Entamoeba spp., and Endolimax mana,andEntamoeba histolytica is one species that may both survive in the colon and be pathogenic, producing amoebic dysentery (Costea et al., 2017).

6. Genito-urinary Tract

6.1. The Urinary System

The kidneys, ureters, bladder, and urethra make up the urinary system. The kidneys function as a specialized filtration mechanism to remove waste products from the blood and selectively reabsorb chemicals that may be utilized again.

6.2. Urine

Normal urine is sterile in adolescents. Organic acids and a negligible number of antibodies are found in normal urine, which is composed of microorganisms. Low pH and high levels of salt and urea inhibit the growth of bacteria in urine. Near the end of its path via the urethra, urine may pick up bacteria from the skin in teenagers.

6.3. Urethra

The area of the urinary system that contains the microbiome is the anterior urethra in male adolescents and the outside entrance of the urethra in female adolescents (Tang, 2017).

Small versions of the same kind of organism seen on the perineum may be found in both sexes' anterior urethras, including Lactobacillus spp, Staphylococcus epidermidis, Haemophilus spp, Bacteroids spp, Cornybacteria spp and Streptococcus spp. The epithelial cells lining the urethra are colonized by facultative anaerobic gram-negative bacteria like Escherichia coli and Proteus mirabilis (Chambers et al., 1987).

The upper portion of the urethra near the urinary bladder has few microorganisms apparently because of some antibacterial effect exerted by the urethra mucosa and because of the mechanical removal of microorganisms by the frequent flashing of the urethral epithelium by urine.

6.4. Vagina

The vaginal environment of a newborn is initially sterile, but within the first 24 hours, it undergoes colonization by nonpathogenic micrococci and enterococci, which may be acquired from the skin, vagina, and intestines. Doderlein's bacillus typically emerges after 2-3 days (Rastogi et al., 2023). The nature of the flora in the vagina depends on the pH of its secretions (Chee et al., 2020). After the passively transferred estrogen has been eliminated in the urine, the glycogen disappears and the pH of the vagina becomes alkaline (Hickey et al., 2015). This brings about a change in the flora. At puberty, the glycogen reappears and the pH changes to acid due to the metabolic activity of bacilli, E. coli and yeast. This change probably helps in the prevention of colonization by possible harmful microorganisms (Moosa et al., 2020).

After menopause, the flora resembles the one found before puberty. That is, vaginal secretions are mildly alkaline and contain normal skin microorganisms. The internal reproductive organs are kept sterile through physical barriers such as the cervical plug of other host defenses (Basis et al., 2023).

7. Importance of microbiome in adolescents

Microbial flora stops or obstructs the invasion of the body by more harmful microorganisms. This exclusion may be accomplished by creating an inhibitory chemical or simply, straightforward competition with the pathogen for nourishment.

• The hydrogen peroxide that Streptococci spp. often produces in the mouth inhibits the growth of other bacteria.

• Colicins, which are often produced by coliform bacteria in the colon, guard the intestinal tract from dangerous microorganisms by suppressing them.

• Normal vaginal Lactobacilli spp. generates lactic acid from the glycogen of the vaginal epithelium. As a result, the vagina is protected against gonococci and other pyogenic organisms by its acidity.

• Propionic acid is produced by the typically occurring Propionibacteria spp. in shin, which helps to keep the pH low and inhibits the growth of infections.

• The body's defensive system may benefit from endotoxin released by gram-negative bacteria by activating an alternative complement pathway.

• The primary B group vitamins, as well as vitamin K and vitamin E, are all produced by the microbes that are often found in the gut, which may help with the host's nutrition.

8. Emerging trends for microbiome analysis and research

An increasing body of preclinical and clinical research has demonstrated a connection between the healthy development of the adolescent brain, metabolism/adiposity, skeleton and gut flora. Future omics studies are necessary to identify the mechanisms by which the gut microbiota of adolescents controls normal development and maturation (Issac et al., 2019). The identification of potential microbial communities that facilitate development and maturation necessitates advanced microbiome sequencing investigations. To explain the practical significance of the gut microbiota in the growth of adolescents, metatranscriptomic research is required (Carson et al., 2023). Furthermore, studies on the metabolome are required to comprehend how the gut microbiota of adolescents controls intestinal and circulatory concentrations of metabolites produced by bacteria that affect the development and growth of healthy adolescents (Zhang et al., 2023). Finally, further research is needed to clarify the ways in which the host and gut microbiota compounds interact to influence skeletal, metabolic, and neurologic development in adolescence. In order to optimize healthy growth and maturation, noninvasive microbiome-based therapies will be supported by an understanding of how the gut microbiota of adolescents influences host development. Probiotics, postbiotics, synbiotics, and prebiotics are examples of noninvasive therapies. By altering the makeup, structure, and activity of the gut microbiota, these microbiome-based therapies can improve health. Interestingly, studies on noninvasive gut microbiota therapies in adolescent healthy subjects have not been conducted. Future studies are thus required to clarify the effects of prebiotics, probiotics, synbiotics, and postbiotics on the development and maturation of healthy adolescents, as well as whether or not these benefits last a lifetime.

Conclusion

Adolescence in humans is undoubtedly one of the difficult stages of growth. Amidst tremendous physiological change and growth, the young adult becomes subjected to a range of stresses and environmental factors. Human teenage years are considered to be a difficult stage of development; during this time, a young person is frequently subjected to an array of psychological stressors, frequently receives nutrition and sleep that falls short of ideal levels and has a higher chance of being exposed to substances known to be neurodevelopmental teratogens like alcohol and drugs. The resident flora is a term used to describe the microorganisms that typically live in a given bodily place (Carson et al., 2023). A person's own cells are outnumbered by the local flora by a factor of 10 to 1. Transient flora refers to microorganisms that inhabit humans for a few hours to many weeks but do not remain there permanently. Each site's native flora consists of a variety of microorganisms (Hitch et al., 2022; Fan & Pedersen.,; 2021). Some places often have hundreds of different species of microbes colonizing them. The organisms that make up a person's resident flora are influenced by environmental variables such as nutrition, antibiotic usage, sanitary conditions, air pollution, and hygiene practices. If momentarily disturbed, the local flora often quickly recovers. The local flora frequently defends the body from pathogenic organisms rather than spreading illness (Fassarella et al., 2020). However, the microbiome has also been potentially linked with some diseases and physiological conditions, viz. inflammatory bowel syndrome,Clostridium difficileinfection, etc.(Dwivedi et al., 2022). An in-depth exploration of the rare microbiota like anaerobes, viruses, and phages and the complex interplay of these microbiomes with host is required to understand the complete functionality and importance of these tiny inhabitants. In this direction, newer omics-based approaches, such as metagenomics and transcriptomics, are proving to be very helpful.

Reference