Epidemiology Notes - HOSA

The Human Microbiome

  • Human body hosts a vast number of microbes, outnumbering human cells 10 to 1.

  • Microbes are crucial for synthesizing nutrients, combating pathogens, and influencing weight and brain development.

  • The Human Microbiome Project aims to catalog these microbes and sequence their genomes.

  • Over 1,000 different microbial species are believed to inhabit the human body.

    • 25 species found in the stomach include:

      • Helicobacter pylori

      • Streptococcus thermophilus

    • 500-1,000 species in the intestines include:

      • Lactobacillus casei

      • Lactobacillus reuteri

      • Lactobacillus gasseri

      • Escherichia coli

    • 600+ species in the mouth, pharynx, and respiratory system include:

      • Streptococcus viridans

      • Neisseria sicca

      • Candida albicans

      • Streptococcus salivarius

    • 1,000 species found on the skin, including:

      • Pityrosporum ovale

      • Staphylococcus epidermidis

      • Corynebacterium jeikeium

      • Trichosporon

      • Staphylococcus haemolyticus

    • 60 species identified in the urogenital tract include:

      • Bacteroides fragilis

      • Bacteroides thetaiotaomicron

      • Lactobacillus rhamnosus

      • Clostridium difficile

      • Ureaplasma parvum

      • Corynebacterium aurimucosum

Symbiotic Relationships

  • Three Types of Symbiotic Relationships:

    • Mutualism: Both organisms benefit; an example includes bacteria in the human colon.

    • Commensalism: One organism benefits while the other is neither helped nor harmed; e.g., Staphylococcus on human skin.

    • Parasitism: One organism benefits at the expense of the other; for instance, tuberculosis bacteria in the human lung.

Normal Microbiota

  • Refers to organisms that colonize the body without normally causing disease.

  • Types of Microbiota:

    • Resident Microbiota:

      • Normal/prolonged residents of specific body areas (skin, mucous membranes, vagina, gut).

      • Can change over time or become harmful if they enter new areas.

    • Transient Microbiota:

      • Temporarily present; picked up from the environment and often eliminated by competition with resident bacteria or hygiene.

Functions of the Microbiome

  • Nose:

    • Mucus production

    • Antimicrobial chemicals

  • Mouth:

    • Assists with digestion and wards off pathogens

  • Lungs:

    • Lubricates pulmonary tissues

  • Stomach:

    • Prevents gastric complications

  • Colon:

    • Digests complex carbohydrates

  • Skin:

    • Strengthens the immune system and contributes to scent production

  • Sexual Organs:

    • Maintain pH levels and produce H₂O₂ to kill microbes

Resident Microbiota

  • Table showcasing various anatomical sites and the common genera found:

    • Skin:

      • Gram-positive: Staphylococcus (including S. aureus), Propionibacterium, Streptococcus, Corynebacterium

      • Gram-negative: Bacteroides, Prevotella, Haemophilus

      • Fungi: Candida

    • Gastrointestinal Tract:

      • Mainly anaerobes with some facultative anaerobes.

    • Oral Cavity:

      • Predominantly Streptococcus

    • Respiratory Tract:

      • Include Moraxella and Prevotella

    • Urogenital Tract:

      • Primarily Lactobacillus in females, with the remainder being sterile.

Factors Influencing Microbiome

  • Development usually starts at birth; womb is generally sterile.

  • Early life establishes normal microbiota, which can change based on various factors, including diet, hygiene, and lifestyle.

  • Internal tissues such as the heart, liver, kidneys, etc., are considered sterile under normal conditions.

Disease and Infection

  • Pathogenicity: The ability of a microbe to cause disease.

  • Virulence: Degree of pathogenicity, illustrated with examples such as the cold versus COVID-19.

  • Common Portals of Entry for Infection:

    • Skin, mucous membranes, and placenta

    • Methods of Infection:

      1. Contamination - mere presence of microbes.

      2. Infection - when organisms establish in the body, possibly resulting in disease.

Factors Weakening Host Defenses

  • Factors that might weaken the body's defenses include:

    • Old age and extreme youth

    • Poor hygiene

    • Genetic conditions

    • Stress and other diseases

    • Certain medications or surgeries

Microbial Mechanisms of Pathogenicity

  • Pathogenicity and virulence are influenced by numerous factors, including:

    • Adhesion Factors: Facilitate attachment to host tissues.

    • Toxins: Chemicals that injure host tissues or trigger immune responses.

      • Exotoxins (produced by living bacteria):

        • Highly toxic, often target specific tissues.

      • Endotoxins (part of Gram-negative bacteria):

        • Less toxic, released upon bacterial death.

  • Extracellular Enzymes: Help bacteria invade and thrive within the host by dissolving structural chemicals.

Emerging Infections and Public Health

  • Diseases that are increasing in presence or potential can arise due to various factors, including genetic recombination, modern transportation, environmental changes, and public health failures.

  • Notable examples include diseases like COVID-19, measles, and antibiotic-resistant strains of bacteria.

The Human Microbiome

The human body is a complex ecosystem that hosts a vast number of microbes, outnumbering human cells by a ratio of approximately 10 to 1. These microbes comprise bacteria, viruses, fungi, and archaea and play essential roles in maintaining human health. They are crucial for synthesizing vital nutrients, combating pathogens, regulating metabolism, influencing weight, aiding in the development of the brain and immune system, and even affecting mood and behavior.

Human Microbiome Project

The Human Microbiome Project is a major initiative aimed at cataloging the diverse array of microbes that inhabit the human body. This project involves sequencing the genomes of these microbes to understand their functions, interactions, and impacts on human health and disease. Over 1,000 different microbial species are believed to reside in the human body, with individuals harboring unique microbial communities.

Microbial Populations by Body Area

  1. Stomach: Approximately 25 species identified, including:

    • Helicobacter pylori (linked to stomach ulcers)

    • Streptococcus thermophilus (used in yogurt production)

  2. Intestines: Host 500 to 1,000 species of bacteria, such as:

    • Lactobacillus casei (beneficial for digestion)

    • Lactobacillus reuteri (known for its probiotic properties)

    • Escherichia coli (some strains are pathogenic, while others are beneficial)

  3. Mouth, Pharynx, and Respiratory System: Over 600 species, including:

    • Streptococcus viridans (commonly found in dental plaque)

    • Neisseria sicca (part of the normal oral flora)

    • Candida albicans (a yeast that can cause infections under certain conditions)

  4. Skin: More than 1,000 species, comprising:

    • Pityrosporum ovale (linked to skin conditions)

    • Staphylococcus epidermidis (normally harmless, but can be opportunistic)

    • Corynebacterium jeikeium (often resistant to antibiotics)

  5. Urogenital Tract: 60 identified species, including:

    • Bacteroides fragilis (important for digestion)

    • Lactobacillus rhamnosus (protects female genital tract from infections)

Symbiotic Relationships

The interactions between humans and their microbiota can be categorized into three types of symbiotic relationships:

  • Mutualism: Both organisms benefit (e.g., gut bacteria aiding in digestion and providing vitamins).

  • Commensalism: One organism benefits while the other is unaffected (e.g., Staphylococcus on human skin).

  • Parasitism: One organism benefits at the expense of the other (e.g., tuberculosis bacteria that can harm lung tissue).

Normal Microbiota

Normal microbiota refers to organisms that colonize the body without normally causing disease. They can be divided into two categories:

  • Resident Microbiota: These are long-term inhabitants of specific body areas such as the skin and gut, whose composition can change with factors like diet or health status.

  • Transient Microbiota: These are temporary inhabitants that are picked up from the environment and eliminated based on competition or hygiene practices.

Functions of the Microbiome

  • Nose: Mucus production and secretions of antimicrobial chemicals help protect against pathogens.

  • Mouth: Assists in digestion and wards off potentially harmful bacteria.

  • Lungs: Lubricates pulmonary tissues, aiding in respiratory functions.

  • Stomach: Helps protect against gastric complications from harmful microbes.

  • Colon: Critical for digesting complex carbohydrates and producing short-chain fatty acids that nourish colon cells.

  • Skin: Strengthens the immune system and contributes to scent production to attract mates.

  • Sexual Organs: Maintain pH levels and produce hydrogen peroxide (H₂O₂) to kill invading microbes.

Factors Influencing the Microbiome

Microbiome development usually starts at birth; the womb is generally sterile. Early life events, maternal microbiota, feeding practices (breastfeeding vs. formula), antibiotics, and exposure to the environment all shape the development and composition of an individual's microbiota. Internal tissues such as the heart, liver, and kidneys are considered sterile under normal conditions.

Disease and Infection

  • Pathogenicity: The ability of a microbe to cause disease, while virulence refers to the degree of pathogenicity, illustrated by examples such as the flu versus more severe infections like COVID-19.

Common Portals of Entry for Infection

  • Skin, mucous membranes, the respiratory tract, and placenta, which microbes exploit to enter the body.

Methods of Infection

  • Contamination: The mere presence of microbes.

  • Infection: When organisms not only enter but also establish themselves in the body, potentially leading to disease.

Factors Weakening Host Defenses

Many factors can compromise the body's defenses, including:

  • Age, particularly the very old and very young

  • Poor hygiene practices

  • Genetic predispositions and conditions

  • Chronic stress and pre-existing diseases

  • Use of certain medications (e.g., immunosuppressants) or surgical interventions.

Microbial Mechanisms of Pathogenicity

The ability of microbes to cause diseases is influenced by various mechanisms, including:

  • Adhesion Factors: Molecules that facilitate microbial attachment to host tissues, critical for colonization.

  • Toxins:

    • Exotoxins: Poisonous substances secreted by living bacteria; highly toxic and often target specific tissues.

    • Endotoxins: Less toxic, released from Gram-negative bacteria upon bacterial death, which can trigger widespread inflammatory responses.

  • Extracellular Enzymes: Molecules that help microbes invade and thrive within the host by breaking down host cell barriers.

Emerging Infections and Public Health

Diseases that are on the rise can result from various factors, including genetic changes in pathogens, modern transportation facilitating the spread of diseases, shifts in environmental conditions, and failures in public health initiatives. Notable examples of emerging infections include COVID-19, measles, and antibiotic-resistant strains of bacteria. An understanding of the human microbiome is crucial in addressing these public health challenges and developing effective prevention and treatment strategies.