Microbiology of dental caries

Question 1

what is the word for when microbes find a new host and start to multiply

Answer 1

colonisation

Question 2

what results when a balance develops between colonised microbes and humans

Answer 2

normal flora

Question 3

what is the word for if microbe causes disease

Answer 3

infection

Question 4

what term do you give if the source of disease is patient’s own flora

Answer 4

endogenous infection

Question 5

what term do you give if the source of disease is from outside patient’s own body

Answer 5

exogenous infection

Question 6

is caries an exogenous or endogenous infection

Answer 6

endogenous

Question 7

what is dental plaque

Answer 7

a diverse microbial community (predominantly bacteria) found on the tooth surface, embedded in a matrix of polymers of bacterial and salivary origin

Question 8

what is the main aeitiological agent associated with caries

Answer 8

plaque

Question 9

where is the oral microbiome mostly

Answer 9

hard tissues

• also on dorsum of tongue
• a bit on soft tissues

Question 10

how many species of bacteria make up the oral microbiome

Answer 10

at least 700

Question 11

how do you accumulate an oral microbiome

Answer 11

sterile at birth

- via food, milk, water and mothers saliva

Question 12

what is the process by which an oral microbiome accumulates

Answer 12

1. colonisation by pioneer bacteria
2. outgrowth
3. secondary colonisation
4. climax community

Question 13

what species of bacteria are mainly the pioneers

Answer 13

streptococcus

Question 14

how is the oral microbiome largely shaped

Answer 14

by their environment i.e. what you feed them

Question 15

how is the oral microbiome formed

Answer 15

• wide variety of microbes regularly enter the oral cavity
• saliva, pH, temp, immune system prevent many species from surviving
• brushing and flossing teeth 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

Question 16

in brief terms what is caries

Answer 16

• 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)

Question 17

what factors make someone low caries risk (bactiera wise)

Answer 17

• alkalia producing bacteria such as S. sanguinis
• unstimulated saliva flow of >1ml/min
• infrequent sucrose consumption
• fluoride intake to levels allowing production of fluorapatite

Question 18

what factors make someone high caries risk (bacteria wise)

Answer 18

• acid producing bacteria such as mutans streptococci and lactobacilli
• unstimulated saliva flow of <0.7ml/min
• frequent consuption of high levels of sucrose and other fermentable carbohydrates
• little or no fluoride intake

Question 19

describe caries progression

Answer 19

1. adhesion
2. survival and growth
3. biofilm formation
4. complex plaque
5. acid
6. caries

Question 20

watch this video, it’s very good

Answer 20

https://www.youtube.com/watch?v=incvTfw6FyA

Question 21

what are the key cariogenic bacteria

Answer 21

STREPTOCOCCUS MUTANS!
Also:
- lactobacillus acidophilus
- actinomyces viscosus
- candida albicans
- nocardia spp
(many others too- 16S sequencing)

Question 22

what is the pH at which the switch between demineralisaion and remineralisaion happens

Answer 22

pH 5.5

Question 23

what drives demineralisaion

Answer 23

microbial metabolism

Question 24

what are the virulence factors associated with bacteria

Answer 24

• pili
• capsule
• flagella
• changes in cell wall composition
• release of endotoxins
• production of exotoxins

Question 25

what are factors related to the cariogenocity of strep mutans (see slide for full)

Answer 25

• produces polysaccharides when you give it sucrose
• can live in pH and produce acid
• good at metabolising sugars
• can drive pH to below 5.5 more rapidly than other species
• can induce caries with it

Question 26

what are the 4 koch’s postulates

Answer 26

1. microbe must be present in every case of the disease
2. microbe must be isolated from the diseased host and grown in pure culture
3. the disease must be reproduced when a pure culture is introduced into a susceptible host
4. the microbe must be recovered from an experimentally infected host

Question 27

key features of strep mutans

Answer 27

1. gram-positive coccus
2. 8 serotypes
3. adhesion and biofilm formation
4. metabolizes dietary sucrose to form insoluble polymers of glucose (stick to surfaces)
5. survive in low pH environments (enamel dissolution)

Question 28

what things combine with S.mutans to give degredation and result in a self fulfilling prophecy

Answer 28

glucans
adhesion
lactic acid

Question 29

what are specific virulence factors associated with s.mutans

Answer 29

1. Adhesions
   - SpaP (makes up fibrillar layer of cell wall)
2. Binding proteins
   - glucosyltransferases, frucosyltransferases, glucan binding protein
3. Sugar modifying enzymes
   - fructanase, dextranase
4. Polysaccharides
   - protection (matrix) and storage (glycogen)
5. Acid tolerance and adaptation
   - ATPase (F1F0ATPase or H+ATPase) (protein pumps which fire out hydrogen ions)

Question 30

describe sucrose metabolism

Answer 30

(watch that video)

sucrose is broken down by frucosyltransferase into fructans and glucose, also by glucosyltransferase into glucans and fructose. These products as well as fructanase result in glycolysis.
Glycolysis produces CO2 as a byproduct which can also drive acid production. Glucans and fructans are very sticky so bacteria can stick to them

Question 31

what are properties of glucans

Answer 31

Water soluble glucans

• readily degraded for energy source
• formation of lactic acid

Water insoluble glucans

• sticky and hard (acts as cement)
• promote accumulation of plaque

Question 32

what acids are responsible for the drop in pH

Answer 32

• lactic acid (strongest as pH3.5)
• formic acid
• acetic acid

Question 33

in what ways is s.mutans acid tollerant

Answer 33

1. maintain pH balance
   - extrusion of H+ ions through a proton translocating F1-F0 ATPase
2. alters cell membrane
   - increase in the proportion of mono-unsaturated membrane fatty acids (decreased proton permeability)
3. protection and repair mechanisms
   - up-regulation of molecular chaperones, proteases and DNA repair mechanisms

Question 34

how does F interfere with acid tolerance

Answer 34

Internally (in the bacterial cell), F inhibits atpase pump so hydrogen can’t keep pumping out

Externally, fluoride ions interact with hydrogen ions to give HF

Question 35

what are the anti-caries activites of fluoride

Answer 35

1. systemic effect
   - incorporation of ingested fluoride into developing enamel as fluoriapatite which reduces its solubility in acid and promotes remineralization
2. topical effect
   - the surface layer of enamel is converted into fluorapatite which reduces its solubility in acid and promotes remineralization
3. antimicrobial effect
   - fluoride inhibits plaque metabolism and is concentrated within plaque. Activity increases at pH values <5, especially in the case of Strep mutans

Question 36

what environmental fluctuations shift towards perio problems

Answer 36

High protein diet

• few acidogenic organisms -> ammonia produced
• more gram-negatives
• secondary metabolites (malodour)

Question 37

what environmental fluctuations shift towards caries problems

Answer 37

High carbohydrate diet

• metabolism reduces pH
• aciduric organisms thrive
• streptococci and lactobacilli