BK - Gut Ecology Flashcards
Where do biofilms cause the most trouble?
Biofilms, slimy communities of bacteria, can wreak havoc in various parts of the body:
Primary sites:
- Mouth: Dental plaque formation leading to cavities and gum disease.
- Subcutaneous tissues: Infections around catheters and implanted devices.
Secondary sites:
- Brain: Can cause meningitis.
- Kidneys: Can lead to urinary tract infections (UTIs).
- Spine: Can cause infections between vertebrae.
How does dental plaque wreak havoc? (3)
Bacteria: Streptococcus mutans and others ferment sugars, producing acids that erode teeth (cavities)
Biofilm structure: Plaque forms a sticky layer, protecting bacteria from the immune system and making removal difficult
Consequences: Cavities, gum inflammation (gingivitis), and gum tissue destruction (periodontitis).
Biofilms and medical devices (2)
- Catheters and implants can provide a surface for bacteria to adhere and form biofilms.
- Biofilms on these devices can lead to serious infections that are difficult to treat
What other organs can be affected by biofilm infections? (3)
- Heart valves (endocarditis)
- Urogenital tract (STIs like gonorrhea, syphilis)
- Bones (osteomyelitis)
What is the oral microbiome and how can it become imbalanced?
The oral microbiome is a complex community of bacteria in the mouth. It can shift from a healthy state to a disease-causing one (dysbiosis)
How does the body defend itself from harmful oral bacteria? (3)
The body employs various physical and chemical barriers to maintain oral health:
- Physical: Keratinized epithelium (skin lining), mucin production (lubricating mucus), and salivary flow (washing away debris).
- Chemical: Enzymes and antibacterials in saliva, and gingival fluid secretions containing immune components
- Inflammatory reaction
How do babies acquire their oral flora?
Acquisition of the Oral Flora (Early)
- Acquisition of oral flora depends upon exposure at the time of birth, cesarean or vaginal. Shortly thereafter, caregivers provide the next insult of microorganisms
Acquisition of the Oral Flora (Later)
- After tooth eruption: organisms favouring hard tissue e.g. Strep. sanguis and Strep. mutans, Actinomyces spp.
Colonisation of crevicular tissues: anaerobic organisms e.g. Prevotella spp.
Loss of teeth: “a 2nd childhood microflora”
Prosthetic appliance: e.g. dentures - similar to enamel plaque, may harbor large numbers of yeast
What is dental caries (cavities) and what factors contribute to it?
Cavities are holes in teeth caused by acid erosion
- High sugar intake and poor oral hygiene are major risk factors.
How does gingivitis differ from periodontitis?
- Gingivitis is gum inflammation caused by plaque buildup and poor hygiene
- Periodontitis is a more advanced stage with bone loss, often linked to specific bacteria
How do Streptococcus mutans bacteria contribute to cavities? (4)
Streptococcus mutans possess several virulence factors that promote cavities:
- Saccharolytic: Break down sugars into acids (acidogenic).
- Glucosyltransferases: Produce sticky glucans that form plaque biofilm (glucosyltransferase).
- Fructosyltransferases: Contribute to plaque formation (fructosyltransferase).
- Acidogenic: Ferment sugars to lactic, acetic, and formic acids, lowering the pH and eroding tooth enamel (aciduric)
What is the role of Veillonella in the oral cavity? (3)
- Gram-negative anaerobic cocci.
- Thrives in the acidic environment of caries and is thought to slow the development of dental caries.
- Converts the lactic acid of other species to less acidic products.
How are Lactobacillus bacteria associated with dental caries? (4)
- Gram-positive facultative anaerobes.
- Normally symbiotic in humans and found in the gut flora.
- Some species with increased numbers in plaque associated with carious lesions.
- “Microbial indicator of disease state” (with S. mutans etc)
What role do Fusospirochetes play in oral health?
In cases of bleeding gums, Fusospirochetes can contribute to infection and diseases like:
- Acute necrotizing ulcerative gingivitis (ANUG) - also referred to as “trench mouth”
- Vincent’s angina.” It’s caused by a combination of anaerobic bacteria including Prevotella intermedia, Fusobacterium, Treponema, and Borrelia spp
What are the three main bacterial culprits in chronic periodontitis?
Treponema denticola
- Gram-negative anaerobic spirochete.
- Elevated levels are found in patients with periodontitis.
- Considered the most important of the three due to its motility and highly proteolytic nature, contributing to tissue destruction.
Porphyromonas gingivalis
- Gram-negative oral anaerobe strongly associated with chronic adult periodontitis. Produces a number of well-characterized virulence factors.
Aggregatibacter actinomycetemcomitans
- Gram-negative facultative non-motile rod, association with localized aggressive periodontitis in young adolescents and bone loss.
- Virulence factors: leukotoxin kills PMNs and moncytes; cytolethal distending toxin; immunosuppression factors that inhibit blastogenesis, antibody production and activate T-suppressor cells
What is the order of colonization in plaque formation? (4)
- Salivary Proteins: Provide an initial adhesive layer on the tooth surface.
- Pioneer Species: Bacteria like Streptococcus mutans attach to the salivary layer, initiating biofilm formation.
- Secondary Colonizers: Species like Veillonella join the community, creating a more complex structure.
- Tertiary Colonizers: Further diversify the biofilm with a wider range of bacterial species.
How do bacteria in plaque measure and respond to their population density? (2)
Bacteria use a chemical signaling system called quorum sensing to communicate and coordinate biofilm formation:
- Intra-species: Gram-positive oral bacteria produce small peptides like competence-stimulating peptides to promote biofilm formation within a single species.
- Inter-species: Mediated by 4, 5-dihydroxy-2, 3-pentanedione (DPD), also called Autoinducer-2 (Al-2). This molecule stimulates plaque formation and virulence factors in various bacterial species.
How can Helicobacter pylori cause stomach ulcers?
H. pylori neutralizes stomach acid with an enzyme (urease) and creates ulcers by damaging the stomach lining
What else does H.pylori do? (2)
Toxin production:
- Produce toxins such as vaculating cytotoxin A (VacA) that kill cells in the lining of the stomach.
- Allows bacteria to better access of nutrients as it decreases the competition from stomach lining cells. vacA mutants are less inflammatory/colonisers
Cell Invasion:
- Invade protective inner lining of the stomach so can be protected from immune system.
- Kill the cells they invade, creating holes in mucus lining of the stomach, causing the formation of ulcers.
How does the early gut microbiome differ depending on feeding method? (2)
Breastfed Babies: Become dominated by Bifidobacteria, possibly due to the presence of bifidobacterial growth factors in breast milk.
Formula-fed Babies: Have a more diverse flora with high numbers of:
- Enterobacteriaceae
- Enterococci
- Bifidobacteria
- Clostridia
- Bacteroides spp
What are some of the major bacterial groups found in a mature gut microbiome and their functions?
Dominant Bacteria:
- Bacteroides (around 30% of all gut bacteria, suggesting its importance).
- Clostridium
- Fusobacterium
- Eubacterium
- Ruminococcus
- Peptococcus
- Peptostreptococcus
- Bifidobacterium
Less Common:
- Escherichia
- Lactobacillus
What are some of the benefits gut microbiota provides to the host? (6)
Fermentation of Unused Energy Substrates: Breaks down complex carbohydrates that the human digestive system cannot process on its own, providing additional nutrients.
Training the Immune System: Helps develop and modulate the immune system, distinguishing between harmless and harmful microbes.
Preventing Growth of Harmful Bacteria: Creates a competitive environment that inhibits
Regulate the development of the gut
Produce vitamins for the host (biotin and vitamin K)
Produce hormones to direct the host to store fats
How does gut microflora play a role in early gut development?
Microflora is essential for promoting the early development of the gut’s:
- Physical components: Gut mucosal structure.
- Immune system function: Both in its physical makeup and how it functions.
How does gut flora help the immune system fight pathogens? (2)
Microflora stimulates the gut-associated lymphoid tissue (GALT) to produce antibodies against pathogens. This allows the immune system to:
- Recognize and fight harmful bacteria.
- Develop a tolerance for helpful bacterial species encountered in infancy.
What are PRRs and how do they help the gut differentiate between bacteria? (2)
PRRs are located on immune cells in the gut lining and help differentiate between:
- Beneficial bacteria: Essential for a healthy gut.
- Pathogenic bacteria: Harmful and cause disease.
