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BDS3 > Microbiology > Flashcards

Microbiology Flashcards

1
Q

What are the ecosystems in the mouth that harbour bacteria?

A
  • Buccal epithelium
  • Dorsum of tongue
  • Gingival sulcus (subgingival tooth surface + GCF fluid)
  • Supragingival tooth surface

Soft tissues: biomass restricted due to shedding

  • Tongue: papillae may act as reservoir
  • Teeth: non-shedding, allow large numbers of microbes
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2
Q

What can hamper study of oral microbes?

A
  • Complexity of flora
  • Fastidious nature of organisms
  • Type can vary over time at a particular site
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3
Q

What are some methods for studying oral microbes?

A

Direct microscopic examination

Microbial culturing

  • Non selective media
  • Selective media

Isolate identification/biochemical classification/taxonomy (e.g. colony morphology)

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4
Q

Is redox usually higher or lower in anaerobic environments?

A

Lower

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5
Q

What role can saliva proteins play?

A
  • Nutrient supply for micrboes
  • Aggregation + swallowing of microbes
  • Inhibit growth of exogenous organisms
  • Antibodies
  • Protective peptides such as histatins (antibacterial and antifungal)
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6
Q

What are some properties of GCF?

A
  • Exude from JE
  • Flow 0.3 microL/hour/tooth
  • Flow removes non-adherent cells
  • Nutrition for microbes
  • Defence (IgG dominant) + leukocytes (neutrophil dominant)
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7
Q

What factors in the oral cavity can influence bacterial growth?

A

-Temperature: Most commonly mesophiles occupy oral cavity, elevated temp e.g. during inflammation can alter gene regulation

pH: Most have optimal growth between 6.5-7.5. Selection for low pH favours acidogenic/duric. Periodontal pockets tend to have higher pH

Redox potential: oxygen levels in environment

  • Obligate Aerobe
  • Microaerophilic
  • Facultative anaerobe
  • Obligate anaerobe
  • Capnophilic (need CO2)

Nutrient supply

  • Saliva (amino acids, peptides, glycoproteins, vitamins)
  • GCF (proteins, hemin)
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8
Q

Why is bacteria responsible for perio disease normally basophilic?

A

-Rely more on peptides/proteins for nutrients which produces alkaline end products

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9
Q

How can different glycosidases from various species work together?

A
  • Glycosidase from one bacteria designed to cleave off end
  • Glycosidase from second bacteria designed to cleave off next monomer and so on
  • In this way, the multiple glycosidases present allow access to more monomers in the chain
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10
Q

What is the role of GTF and FTF?

A

Play roles in EPS metabolism:

FTF:

  • Break down sucrose into glucose/fructose
  • Glucose uptaken into cell
  • Forms fructans (long chain polymers) from fructose that can contribute to EPS
  • In times of starvation, fructanase breaks down fructan to release fructose for nutrients

GTF:

  • Break down sucrose into glucose + fructose
  • Fructose taken up into cell
  • Forms glucans from glucose, consisting of two types
  • Glucans (1-6 linkage) are water soluble and function in adding to bulk of plaque + formation of water channels + aggregation
  • Mutans (1-3 linkage) water insoluble and sticky, function in adherence to tooth/important in smooth surface caries
  • In times of starvation, dextranases breakdown glucans for glucose supply

*GTF’s also function in attaching to acquired pellicle nad producing polymers that allow cells to attach

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11
Q

How can milk influence bacterial growth?

A
  • Acts as buffering agent
  • Reduce adherence of GTF adsorption to pellicle->decrease S.mutas adherence
  • Ca and PO4 may provide remin
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12
Q

How can cheese influence bacterial growth?

A

-Stimulate salivary flow and raises pH

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13
Q

How can saliva antagonise microbes?

A
  • Flushing
  • Enzymes: peroxidases + lysozyme
  • Antibodies
  • Mucins + agglutinins
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14
Q

How can GCF antagonise microbes?

A
  • Flow rate
  • Antibodies
  • Complement
  • Polymorphs
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15
Q

How can oral mucosa protect itself from bacteria?

A

Physico-chemical

  • Mucins
  • Intra-epithelial barrier
  • Basement membrane

Immunological:
sIgA + serum IgG (prevent adhesion, opsinise, complement)
Langerhans cells (prevent adhesion and metabolism)
Intraepithelial lymphocytes (cellular barrier)

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16
Q

What are the main triggers for oral bacterial disease?

A
  • Opportunistic pathogen at foreign site (endo)

- Change in proportions (caries)

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17
Q

How are bacteria classified?

A 
Kingdom 
Phylum
Genus
Species
Serotype
Strain
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18
Q

How to differentiate between strep and staph

A

Strep=catalase negative

Staph=catalase positive

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19
Q

What bacteria are responsible for early stages of caries

A

Mutans group

NOT strep mutans species

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20
Q

What bacteria can be transmitted from mother to child?

A

-S.salivarius and mutans streps

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21
Q

What are some characteristics of actinomyces?

A
  • Most dominant G+ rod in plaque
  • Short rods with branching filaments
  • Found in gingival crevice and interproximally
  • A.naeslundii is a pionner plaque organism and serves to form extracellular polymer from sucrose
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22
Q

What are some characteristics of Lactobacillus?

A
  • gram +
  • Have both oxidative and fermentative metabolism
  • Homofermentative or heterofermentative
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23
Q

What are some characteristics of rothia dentocariosa?

A
  • Gram +
  • Supragingival
  • Fermentative (lactate and acetate)
  • May be involved in endocarditis
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24
Q

What are some characteristics of bifidobacterium?

A
  • Gram +
  • Subgingival
  • Reduce redox by producing hydrogen which reacts with oxygen to produce water
  • Non proteolytic and asaccharolytic: likely scavengers from more aggressive bacteria
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25
Q

What are some characteristics of staphylococcus?

A
  • Gram +
  • Catalase +
  • Fermentative
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26
Q

What are some characteristics of streptococci?

A
  • Gram +
  • Can be alpha (partial), beta (complete) or gamma haemolytic (no hb breakdown)
  • Main groups are mutans and mitis groups (named after the most common species in each group), i.e. Mutans group contains S.mutans species
  • Facultative anaerobes (may ferment sorbitol and mannitol)
  • Produce extracellular polysaccharides from sucrose (in particular mitis group important in adhering to tooth/plaque establishment)
  • Produce intracellular polysaccharides
  • Acidogenic + duric
  • Mutans and sobrinus most implicated in caries
  • Salivarius can produce extracellular fructose
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27
Q

What are some characteristics of the Strep. Mitis Group? (not the species)

A

Gram +

  • Mitis/S.sanguis produce EPS and IgA protease
  • Mitis/gordonii Binds amylase
  • Mitis/oralis: Bind IgA

-All produce EPS, thus making them all early colonisers

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28
Q

What are some properties of P.gingivalis?

A
  • Gram -
  • Obtains energy from amino acids, produces ammonia as an end product
  • Produces trypsin-like proteases
  • Produces haemolysins
  • Has attachment fibrils
29
Q

What are some properties of T forsythensis?

A

Gram -

  • Fusiform shape (tapers at ends)
  • Ferments glucose poorly
  • Has trypsin like activity
  • Implicated in perio disease
30
Q

What are some properties of fusobacterium?

A

Gram -

  • Metabolically versatile
  • However slow fermentation of carbonhydrates
  • Can aggregate with many other oral species
  • Found in gngival sulcus
  • Produces sulfur compounds
31
Q

What are the properties of T.denticola?

A
  • Trypsin like activity
  • Spirochaete
  • Degrades collagen (to release proline which is necessary for structure) and gelatin
32
Q

What are some properties of Veillonella?

A
  • Supragingival
  • Can not ferment glucose as lack glucokinase/can not phosphorylase
  • Can use lactic acid
  • Originally thought to be protective but acid already released
33
Q

How can AIDS and antibiotic therapy increase risk of oral fungi?

A
  • Immunosuppression

- Killing of competing bacteria

34
Q

What are the roles of saliva?

A
  • Anti fungal, bacterial, viral
  • Remineralisation
  • Tissue coating
  • Lubrication
  • Digestion
  • Buffering
35
Q

How does the proportion of plaque differe for interproximal plaque?

A

-Increase in actinomyces and obligate anaerobes

36
Q

What are some benefits of biofilms?

A
  • Protection from host defence
  • Protection from dessication
  • Protection from antimicrobials
  • Novel gene expression and phenotype
  • Attachment/resists flushing
37
Q

What is the function of touch sensors in cells?

A

-Senses whether bacteria has touched a surface to allow it to attach

38
Q

What is quorum sensing?

A
  • Senses numbers of bacteria present by detection of concentration of extracellular products produced by bacteria
  • In particular most common is auto-inducers (AI2)
  • Once reach particular quorum, bacteria may express virulent proteins (whereas it has not done so before to avoid host systems, however once numbers high enough can try to invade host)
39
Q

How does dental plaque develop?

A
  • Adsorption of bacterial/host products to tooth (acquired pellicle)
  • Transport of microbes to enamel coated surface
  • Adhesion of microbes to pellicle
  • Co-aggregation of microbes to already attached cells
  • Multiplication of microbes
  • Detachment
40
Q

What is the function of early colonisers?

A
  • Lower Eh
  • Release extra nutrients
  • Increase diversity
  • Multiply to form micro-colonies
  • Micro-colonies form confluent growth
41
Q

What are crytitopes?

A
  • Hidden receptors for bacteria cells
  • Exposed after enzymatic action
  • P.gingivalis binds to trypsin treated epithelium
  • Charlie’s analogy: hidden room
42
Q

How can adhesins between different bacteria be blocked?

A
  • Addition of CHO

- treating receptor with protease

43
Q

What is the role of EPS?

A
  • Maintain water channels (allows penetrations of nutrients), concentration of products form a gradient
  • Attachment via GTF
44
Q

What are some beneficial and antagonistic effects in dental plaque?

A

Beneficial:

  • Co-aggregation
  • Food webs (waste from one nutrient to another)
  • Enzyme complementation

Antagonistic:

  • Bacteriocidins
  • Hydrogen peroxidase
  • Compete for nutrients
  • Organic acids
  • pH extremes
45
Q

What can cause breakdown of oral homeostasis?

A
  • sIgA deficiency
  • Neutrophil dysfunction
  • Immune suppression
  • Xerostomia
  • Antibiotics
  • CHO
  • Increased GCF flow
  • Oral contraceptives
46
Q

What are Koch’s postulates for dental caries?

A
  1. Must produce appropriate virulence factors
  2. Must be present in high enough numbers to cause disease
  3. Must be able to reproduce disease in appropriate animal model
  4. Removal of microbe should improve disease
  5. Microbe should be able to generate sufficient antibodies
47
Q

What are Koch’s regular postulates?

A
  1. Microbe should be found in all cases of disease
  2. Can be grown on artificial medium
  3. Pure culture should produce disease in animal
  4. Should detect high antibody titre
48
Q

What are the different caries hypothesis?

A
  • Specific plaque
  • Non specific plaque
  • Ecological plaque
49
Q

What are the main factors for caries?

A

Plaque
Host
Bacteria
Diet

50
Q

Why can antibiotics not be used to treat caries?

A

Not considered life threatining + resistance develop + too late by the time cavitation occurs

51
Q

Why can vaccines not be used to treat caries?

A
  • Too many species, can’t vaccinate every one

- Controversy regarding vaccines, thus not made for caries as not life threatening

52
Q

What role do S.mutans species have on caries?

A

-Initiation of disease/white spot lesion with A.naeslundii

53
Q

What difference in mutans streps development exists between interprox caries and smooth surface?

A

-Interprox: increased MS occurs later and presence is less consistent with disease sites/absence less consistent with healthy sites

54
Q

Which are of the tooth has strongest association with MS and caries?

A

-Fissure occlusal

55
Q

How does dentine infection differ with enamel infection in caries?

A

-More diverse population in dentine

56
Q

What bacteria are responsible for root surface caries?

A
  • Actinomyces
  • Stretopcocci
  • lactobacilli
57
Q

What are some characteristics of bacteria that enable them to produce caries?

A
  • Sugar transport: operate over a wide range of conditions (e.g. low pH)
  • Acid production: efficient glycolytic pathway allowing rapid acid production
  • Aicduricity: Must be able to grow in low pH environments
  • EPS: provides protection, adherence and transport of nutrients
  • IPS: provides emergency store in absence of dietary sugars
58
Q

What are some sucrose uptake systems used by S.mutans?

A 
Sucrose PTS (lowest Km highest affinity)
Trehalose PTS (midway)
Multiple sugars TS (highest Km lowest affinity)
59
Q

What is the mechanism for acid tolerance of strep mutans?

A
  • Uses ATP’ase pumps which pump out H+ ions at the cost of using ATP
  • However if external environment low pH cell is producing lots of acid thus has ATP, so no loss
  • Function at a lower optimal pH for S.mutans than for other cels
  • Down-regulates PTS system, shifts to homo-fermentative metabolism
  • Transmembrane gradient also tends to drive out any undissociated lactic acid
  • Synthesis of stress proteins
60
Q

What is the relation of pKa to acid’s acidity?

A

-Lower pKa=more acidic

61
Q

What factors (upon being removed from bacteria) result in decreased cariogenicity?

A

-GTF production
-IPS production
Lactate dehydrogenase production
-Aciduricty

62
Q

How does fluoride stop caries?

A
  • Inhibit enolase
  • Acidify internal pH
  • Interfere membrane function
  • Reduce IPS
  • Resistance to fluoride results in decreaseds acidogenicity and acidoduricity

-Also remin

63
Q

What are the mecahnisms of chlorhexidine?

A
  • Broad spectrum but do not disturb normal flora
  • Positive charge causes it to adhere to negatively charged bacterial membrane
  • Damages membranes similar to detergents
  • Blocks adherence
  • Inhibits PEP/PTS
  • Blocks ATP’ase
64
Q

What is the mode of action of xylitol?

A
  1. It gets taken up into the cell as cell attempts to use it for energy
  2. As such ATP is used to phosphorylate it into xylitol-5-phospate
  3. However xylitol can’t serve any purpose inside cell
  4. As such build up and risk of reaching toxic levels
  5. Therefore cell spends ATP to de-phosphorylate and push back out
  6. However once back out taken back in again
  7. Therefore futile cycle
65
Q

What is replacement therapy?

A
  • Expose oral environment to colonisers which either colonise the tooth and prevent cariogenic strains taking over or which displace cariogenic strains
  • e.g. Hillman-MS strain produces mutacin to kill other strains
  • Removed LDH replaced with ADH->less cariogenic
66
Q

How does saliva test work?

A
  • Test for presence of mutans streps and lactobacilli using selective media
  • Timing of sampling is important (eg after meal or smoking)
67
Q

What changes occur in bacteria with perio disease?

A
  • Switch from strep to actinomyces
  • Increase capnophilic + gram neg anaerobes
  • A.naeslundii and A.israelii in non-bleeding
  • Bleeding black pigmented anaerobes
  • Increased GCF flow means increased nutrients
  • Reduced redox potential
  • Increase anaerobes + gram -, decreased facultative + gram positive, increase rods
68
Q

What is the main metabolism type for perio bacteria?

A

-Asacchrolytic, anaerobic, liberate ammonia

69
Q

What do glycosidases do?

A

Liberate CHO from glycoproteins

BDS3 (7 decks)

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