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.