Caries microbiology Flashcards
What is the pathogenesis of infection
• When microbes find a new host and start to multiply its called colonisation
• A balance can develop between colonised microbes and humans which is the normal flora
• If microbes cause disease it is an infection, caries is an infection
• If the source of microbe is a patient’s own flora it is called an endogenous infection
If the source of the microbe is flora from outside the patient’s own flora - called an exogenous infection
What is dental plaque
• A diverse microbial community (predominantly bacteria) found on the tooth surface, embedded in a matrix of polymers of bacteria and salivary origin
Plaque is the main aetiological agent associated with caries
Describe the oral microbiome
- At least 700 bacterial species
- Predominantly on hard tissues
- Also found on the dorsum of the tongue and on soft tissues (shedding)
- We are sterile at birth and we acquire bugs through food, milk, water, mother’s saliva etc
Outline plaque formation
- Pellicle formation
- Colonisation by pioneer bacteria (streptococcus species)
- Outgrowth
- Secondary colonisation by other organisms
- Climax community
What are the basic concepts of oral microbiology
- A wide variety of microbes regularly enter the oral cavity
- Host factors effect their growth and prevent many species from surviving
- Brushing and flossing clears some built up biofilm
- Oral antibiotics inhibit growth
- Symbiosis of the oral microbes that are able to survive these conditions form an elaborate scaffold that lives on the tooth enamel and at the interface with the gums
- It forms a barrier for incoming bacteria
What are the host factors
○ Saliva
○ pH
○ Temperature
Immune system
What is caries
• Loss of mineralized surfaces of the tooth
• Surfaces are permanently damaged
• Underlying dentine is at risk or damaged
• Multi-factorial disease
○ Microbial biofilms
○ Acidity, sugar metabolism
What makes someone low risk
○ Alkaline producing bacteria such as S. sanguinis
○ Unstimulated saliva flow >1ml/min
○ Infrequent sucrose consumption
Fluoride intake to levels allowing production of fluorapatite
What makes someone high risk
○ Acid producing bacteria such as mutans streptococci and lactobacilli
○ Unstimulated saliva flow of <0.7ml/min
○ Frequent consumption of high levels of sucrose and other fermentable carbohydrates
○ Little or no fluoride intake
Outline caries progression
- Adhesion
- Survival & growth
- Biofilm formation
- Complex plaque which is difficult to remove
- Acid
Caries and possibly irreversible damage
What are the key cariogenic pathogens
○ Streptococcus mutans ○ Lactobacillus acidophilus ○ Actinomyces viscosus ○ Candida albicans Nocardia spp.
What are the virulence factors of a prokaryotic cell
○ Pili for attachment
○ Capsule which is sticky and protects host immunity
○ Flagellum - swim through bacteria
Endotoxins - released from gram cell walls
Describe caries association with s. mutans
- Produces water soluble and insoluble extracellular polysaccharides from sucrose which help in colonization of the tooth surfaces by consolidating microbial attachment
- Ability to initiate and maintain microbial growth and to continue acid production in sites with a low pH
- Rapid metabolism of sugars to lactic and other organic acids
Can attain the critical pH for enamel demineralisation more rapidly than other common plaque bacteria
What is koch’s postulate
- The microbe must be present in every case of the disease
- The microbe must be isolated from the diseased host and grown in pure culture
- The disease must be reproduced when a pure culture is introduced into a susceptible host
- The microbe must be recovered from an experimentally infected host
Describe s. mutans
- Gram-positive coccus
- 8 serotypes
- Adhesion and biofilm formation
- Metabolizes dietary sucrose to form insoluble polymers of glucose – stick to surfaces
Survive in low pH environments – enamel dissolution
What are gluons
- S mutans can produce glucans which help in it’s adhesion
The more it adheres, the more colonisation and the more acid
What are the virulence factors
adhesins binding proteins sugar modifying enzymes polysaccharides acid tolerance and adaption
What are adhesions
○ Make up fibrillar layer of cell wall
Help to attach to teeth
What are sugar modifying enzymes
Take sugars to make glucans
What are polysaccharides
○ Protection from external environmental forces but also storage (glycogen)
What is acid tolerance and adaption
○ Has membrane pumps (ATPase) within the cell membrane that fire out hydrogen ions
○ As the pH goes down, we can put them straight back out and maintain internal equilibrium at a more neutral pH so it can survive in high acid conditions
Describe sucrose metabolism
- If you feed them sugar, they have enzymes that can produce glucans and fructans and these are very sticky
Glycolysis will take these sugars, produce carbon dioxide and that is the driving part in acid production
What are the types of glucans
water soluble
water insoluble
Describe water soluble glucans
○ Readily degraded for energy source
Formation of lactic acid
Describe water insoluble glucans
○ Sticky and hard - act as cement
○ Promote plaque accumulation
○ Very difficult to remove
What is GBP
- Glucan binding proteins help the bacteria stick to surfaces and to one another
What acids are produced
- Lactic acid - strongest (pH 3.5)
- Formic acid
- Aacetic acid
pH drops below 5.5 leads to demineralization
Describe acid tolerance
maintain pH balance
alter cell membrane
protection and repair mechanisms
How is pH maintained
○ Extrusion of hydrogen ions via the ATPase pump means that it maintains physiological pH levels but this requires energy
How is the cell membrane altered
○ Increase in the proportion of mono-unsaturated membrane fatty acids - decreased proton permeability
What are the protection and repair mechanisms
○ Up-regulation of molecular chaperones, proteases and DNA repair mechanisms
How does fluoride interfere with acid tolerance
- Fluoride can interact with hydrogen ions and become hydrogen fluoride externally
- Internally the fluoride ion decouples and it inhibits the ATPase pump so it kills the bacteria
Antibacterial effect of fluoride
- Internally the fluoride ion decouples and it inhibits the ATPase pump so it kills the bacteria
What are the anti caries activity of fluoride
systemic effect
topical effect
anti microbial effect
What is the systemic effect of fluoride
○ Incorporation of fluoride into developing enamel which reduces its solubility
What is the topical effect of fluoride
Surface layer of enamel converted to fluorapatite which reduces its solubility
What is the antimicrobial effect of fluoride
○ Fluoride inhibits plaque metabolism and is concentrated within plaque
○ Activity increases at pH values <5 especially in the case of s mutans
What is the environment fluctuation of a high protein diet
○ Few acidogenic organisms –> ammonia produced
○ More gram negatives
Secondary metabolites results in malodour
What is the environment fluctuation of a high carb diet
○ Metabolism reduces pH
○ Aciduric organisms thrive
Streptococci and lactobacilli drive cariogenic processe
How do we manage caries microbiology
- Diet is key ○ All carbohydrates not just sweets - High fluoride - Gum for salivary flow - Probiotics (experimental) - Vaccines (experimental) AMP (experimental)
