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GI tract ppt

MICROBIOLOGY (BIOL2038) - Medical Microbiology

2. Gut Ecology

Instructor: Prof Bill Keevil

Learning Outcomes for 2. Gut Ecology

  • Key Diseases Caused by Dental Plaque

    • Understand the major diseases: caries, gingivitis, and periodontitis.

  • Important Streptococci in Early Teeth Colonisation

    • Learn about their ability to form polysaccharides and ferment dietary sugars.

  • Anaerobes Associated with Gingivitis

    • Identify several key anaerobes involved in this disease.

  • Pathogens in Periodontosis

    • Recognize the “big 3” pathogens linked to this condition.

  • Types of Plaque Colonisers

    • Name examples of pioneer, secondary, and tertiary plaque colonisers.

  • H. Pylori Survival Mechanism

    • Explain how it survives stomach acidity and colonises epithelia.

  • Gut Flora in Infants

    • Compare the gut flora of breast-fed versus formula-fed babies.

  • Role of Bacteroides fragilis PSA

    • Describe its role in maintaining healthy flora.

Biofilms & Communities

  • Infection Statistics

    • CDC: 65% of infections are biofilm-related (1999).

    • NIH: 80% are biofilm-related (2002).

  • Historical Perspective

    • Leeuwenhoek observed polymicrobial communities- animacules - dental plaque under microscope

    • Pasteur and Koch focused on isolating single species.

Points of Entry for Bacteria

  • Primary Infection Sites

    • Mouth (infection via bleeding gums).

    • Catheter entries (e.g., subvenous catheter).

    • Implanted devices (e.g., artificial hip joint).

  • Common Areas of Secondary Infection

    • Brain, kidneys, intervertebral spaces, bones around devices.

Medical Problems of Microbial Adhesion

  • Teeth:

    • Plaque flora leads to malodour, tooth decay, gum diseases.

  • Stomach:

    • H. pylori causes gastric ulcers.

  • Intestine:

    • E. coli O157 leads to gastroenteritis.

  • Colon:

    • C. difficile causes gastroenteritis.

  • Upper Respiratory Tract:

    • Ps. aeruginosa is linked to cystic fibrosis.

  • Heart Valves:

    • Streptococci lead to endocarditis.

  • Urethral/Cervical Epithelium:

    • Infections from gonococci, Candida, Treponema.

  • Bone:

    • Infections from staphylococci and streptococci lead to osteomyelitis.

Oral Microbiology

  • Microbial Interactions

    • Over 700 different bacterial groups.

    • Presence of fungi (Candida spp) and mycoplasma.

    • Interaction between microbes and the host can shift from healthy to disease microflora (dysbiosis).

  • Normal Microflora

    • Facultatives: streptococci, lactobacilli, staphylococci; Anaerobes: Bacteroides.

Dental Plaque and Disease

  • Health Conditions

    • Healthy oral flora to gingivitis to caries to periodontitis progression.

  • Inflammation Due to Dental Plaque

    • Leads to gingivitis and periodontal diseases.

Oral Health

  • Equilibrium

    • Balance between endogenous bacteria and oral defence systems:

      1. Physical Barriers: Keratinized epithelium, mucin, salivary flow.

      2. Chemical Compounds: Salivary enzymes, antibacterials.

      3. Inflammatory Reactions: Dynamic interface between host and microbes, with quorum sensing as a communication method.

Acquisition of Oral Flora (Timeline)

  • At Birth: Sterile environment.

  • Hours Post-Birth: Streptococcus spp. colonisation begins.

  • 1 Year: Increase in diverse bacteria, including S. mutans and S. sanguis with tooth eruption.

Bacteria in the Oral Cavity

  • Daily Bacterial Shedding: 1 x 10^8 bacteria.

  • Plaque Composition: 5% salivary flora; >300 species in plaque; 1 mg plaque contains 1 x 10^6 bacteria.

  • Healthy Gingiva Flora: Mainly aerobic and facultative anaerobes; >40% unculturable.

Important Dental Diseases

  • Caries: Linked to high sugar diet and poor hygiene; leads to holes and malodour.

  • Periodontal Diseases:

    1. Gingivitis: Non-destructive, caused by poor hygiene.

    2. Periodontitis: Destructive, often occurs with age or poor hygiene leading to gum and bone loss.

Streptococcal Virulence Factors in Carious Plaque

  • Metabolism Types:

    • Saccharolytic: metabolise sugars.

    • Acidogenic: produce acids that lower pH.

    • Aciduric: survive and thrive at low pH.

Other Species in Plaque

  • Veillonella:

    • Gram-negative anaerobic cocci, slows caries by converting lactic acid.

  • Lactobacillus:

    • Found in normal gut flora; some species linked to caries.

Fusospirochetes and Gingivitis

  • Infections:

    • Conditions such as Acute necrotizing ulcerative gingivitis caused by various anaerobic bacteria.

Periodontitis: The Big 3 Pathogens

  1. Treponema denticola: Key spirochete involved in tissue destruction.

  2. Porphyromonas gingivalis: Strongly linked to chronic periodontitis with virulence factors.

  3. Aggregatibacter actinomycetemcomitans: Associated with aggressive periodontitis; produces leukotoxin and immunosuppressive factors.

Cell-Cell Communication in Biofilms

  • Quorum Sensing: Mediated by signaling molecules for intra- and inter-species interactions.

Anti-Pathogen Strategies

  • Preventing Biofilm Formation: Use of attachment blockers or detachment signals to hinder periodontal pathogens.

Human Microbiome Project

  • Introduction: Follows the Human Genome Project to identify the variety of species across different body sites using molecular techniques.

Helicobacter Pylori: Mechanism of Action

  • Attachment & Survival:

    • Attaches to mucus lining and neutralizes stomach acid via urease.

    • Produces toxins and invades the epithelial lining, causing ulcers.

Intestinal Flora Overview

  • Microbial Density: Approximately 100 trillion microbes in the intestine; metabolic activity comparable to an organ.

  • Diversity: Over 300–1000 species but dominated by a few.

  • Anaerobes: Represent >99% of flora; graduates to strict anaerobes.

Early Gut Microflora Development

  • Colonisation Post-Birth:

    • Influenced by maternal transfer; dominated initially by E. coli and streptococci.

    • Bifidobacterium dominates breast-fed infants.

    • Formula-fed infants show diverse flora.

Symbiotic Relationships in Gut Flora

  • Functions:

    • Ferment unused energy, train immune system, produce vitamins, regulate gut development.

    • Potentially pathogenic under certain conditions.

Dysbiosis and Health Implications

  • Associated Conditions:

    • Link to various diseases such as asthma, obesity, autism, and heart diseases, addressing the role of gut health in systemic conditions.

Gut Flora and Immunity

  • Role of Microflora:

    • Influences the development and function of the immune system, helping to differentiate between beneficial and harmful bacteria.

Pattern Recognition Receptors (PRR)

  • Immunological Role:

    • Help the intestine identify pathogens and initiate defense responses through inflammation activation.

PSA: Microbial Health Factor

  • Capsular Polysaccharides of B. fragilis:

    • Important for immune modulation and restoration of T cell levels.

PSA and Immune Balance

  • Th1/Th2 Balance:

    • Restores immune balance, crucial for gut health; influences cytokine levels and immune responses.

Pseudomembranous Colitis Presentation

  • Clinical Appearance: Visible exudative plaques that can lead to severe gastrointestinal issues due to dysbiosis.

Fecal Transplant Data

  • Effectiveness:

    • Significant cure rates for recurrent Clostridium difficile infections highlighted by various treatment comparisons.

Overt GI Pathogens

  • Common Pathogens:

    • Waterborne and foodborne bacteria including Salmonella, Vibrio, Campylobacter, and Listeria.

Summary of Gut Microbiome

  • Complex Interactions: Emphasizes the importance of a healthy microbiome and the consequences of disrupting it through dietary changes or antibiotics.