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Microbiology for Dentists > 15. Mouth as a Habitat for Microbes > Flashcards

15. Mouth as a Habitat for Microbes Flashcards

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1
Q

Define ‘autochthonous microbiota’

A
  • microorganisms found characteristically at particular site
  • they’re adapted to survive and grow here
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2
Q

Define ‘allochthonous microbiota’

A
  • microorganisms transiently present at site
  • don’t thrive here but may colonise transiently or if site becomes compromised in disease
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3
Q

Relative sizes of oral microbes and structures from smallest to largest

A
  • individual cells
  • chains or filaments of cells
  • candida
  • neutrophils
  • hedgehogs with sweetcorns
  • epithelial cells
  • rotund aggregates
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4
Q

What’s making detection of viruses easier?

A

PCR methods

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5
Q

Viruses present in oral microbe

A
  • bacteriophage
  • herpes simplex type 1 (cold sores) is most common
  • HIV and Hep B can be asymptomatically carried
  • SARS-CoV-2 can replicate
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6
Q

Most common oral virus

A

herpes simplex type 1

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7
Q

Archaea in the mouth

A
  • rarely isolated from healthy individuals
  • detected in periodontal disease
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8
Q

Fungi in oral microbiota

A
  • occasional infections like aspergillus
  • most common are Candida spp.
  • many fungi in low abundance
  • most fungi only infect vulnerable like young, old, cancer - generally we are robust against them
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9
Q

The most important fungi do what?

A

make hyphae

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10
Q

Are viruses in the mouth dangerous?

A

not usually
- control bacterial population
- imapct dental plaque

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11
Q

Any individual has … to … different bacterial species in mouth from 700 … species

A

100-200
allochthonous

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12
Q

3 types of bacteria seen in health in mouth

A
  • obligate aerobes like neisseria
  • facultative anaerobes e.g streptococcus
  • obligate anaerobes e.g veillonella
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13
Q

Bacteria seen in dental caries

A
  • acidogenic, aciduric bacteria
  • like streptococcus mutans
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14
Q

Difference between acidogenic and aciduric

A
  • produce acid
  • tolerate low pH
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15
Q

Bacteria in periodontitis

A
  • obligate anaerobes
  • like treponema denticola
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16
Q

From healthy bacteria in mouth to bacteria in periodontitis, what shift is seen?

A

from gram pos to gram neg bacteria

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17
Q

Give 4 different microbial habitats in the mouth

A
  • lips, cheeks, palate
  • tongue
  • teeth
  • saliva
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18
Q

Explain lips, cheeks, palate as a habitat

A
  • epithelial cells
  • continually shed (desquamation)
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19
Q

Explain tongue as a habitat

A
  • highly papillated
  • resevoir for obligate anaerobes (perio. pathogens)
  • tonsils can harbour these pathogens too
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20
Q

Explain teeth as a habitat

A
  • non-shedding
  • lots of diff surfaces with diff microbial populations
  • covered with acquired enamel pellicle
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21
Q

Explain saliva as habitat

A
  • transient presence in the mouth
  • carries microbes between locations
  • microbes often attached to desquamatised epithelial cells
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22
Q

Do you brush away the acquired pellicle?

A
  • no
  • only removed by vigorous acid washing
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23
Q

What would you see from the mouth and nose on a kiss agar plate?

A
  • alpha-haemolysis by oral streptococci producing water to bleach haemoglobin
  • gamma haemolysis (no haemolysis) at nose as most bacteria here are staphylococcus spp.
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24
Q

Bacteria on tongue

A
  • strep (salivarius/mitis)
  • prevotella
  • actinomyces
  • veillonella
  • haemophilus
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25
Q

Bacteria on cheek

A
  • strep (mitis
  • haemophilus
  • simonsiella
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26
Q

Bacteria on teeth in supragingival plaque

A
  • strep
  • actinomyces
  • haemophilus
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27
Q

Bacteria on palate

A
  • strep
  • actinomyces
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28
Q

Bacteria on teeth in subgingival plaque

A
  • strep
  • actinomyces
  • peptostreptococcus
  • fusobacterium
  • aggregatibacter
  • porphyromonas
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29
Q

Saliva is … when secreted
What then happens?

A
  • sterile
  • rapidly accumulates around 10^9 bacterial cells per ml
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30
Q

Around 3 times more bacteria is attached to … than are free in saliva

A

epithelial cells

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31
Q

3 ways bacteria are removed from oral surfaces

A
  • sloughing of epithelial cells
  • mechanical debridement
  • active release (possible)
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32
Q

How to get a reflection of overall oral microbiome?

A

sample saliva

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33
Q

Limitations of sampling saliva as a reflection of oral microbiome`

A
  • proportions of microbial species are diff from plaque/soft tissue
  • care required when sampling to standardise
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34
Q

How to culture oral microbiota

A
  • isolate bacteria
  • culture on agar
  • estimate number of diff species by culturing and counting colonies
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35
Q

4 reasons we isolate bacteria

A
  • understand basic physiology
  • link organism to disease (Koch’s postulates)
  • identify pathogenesis mechanisms
  • test antibiotics
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36
Q

Explain the Great Plate Count anomaly

A
  • some bacteria are dormant and not easily reactivated
  • some species are fastidious - don’t grow on nutrient agar
  • better to culture from humans but will then miss species
37
Q

Define ‘culture-independent microbial analysis’

A
  • techniques based on comparison of DNA sequences from diff bacteria
38
Q

In culture-independent microbial analysis, do you isolate the organism?

A
  • not required
  • but this can be used to aid isolation and identification
39
Q

2 approaches within culture-independent microbial analysis

A
  • community sampling
  • environmental genomics
40
Q

Explain community sampling in culture-independent microbial analysis

A
  • amplify single gene for example gene encoding 16S rRNA or for specific function
  • sequence and generate a tree
  • get a single gene phylogenetic tree
  • snapshot of most members of a community and diversity of microbial guild
41
Q

Explain environmental genetics for culture-independent microbial analysis

A
  • restriction digest total DNA and shotgun sequence
  • or do it directly using high-throughput DNA sequencer
  • assemble and annotate a total gene pool of community
  • identifies all gene categories, discovers new genes and links genes to phenotype
42
Q

We are holobionts. What does that mean?

A
  • superorganisms of our own cells and our microbiota
43
Q

Define ‘16S ribosomal RNA’

A
  • an RNA molecule around 1500 nucleotides long
  • part of small subunit of ribosome in prokaryotes
44
Q

Define ‘biofilm’

A
  • sessile community of microbes characterized by cells attached to surface or to each other
  • embedded in a extracellular polymeric substances
45
Q

Define ‘bioinformatics’

A

application of computational techniques to analyse complex biological data like genetic codes

46
Q

Define ‘coevolution’

A

parallel evolution of interacting species

47
Q

Define ‘community profiling’

A
  • characterisation of complex microbial communities
  • by their 16S rRNA gene sequences
48
Q

Define ‘dysbiosis’

A

condition in which normal microbiome population structure is disturbed
- often by external burdens like disease or medication

49
Q

Define ‘epigenetics’

A

the study of heritable changes in gene expression not caused by changes in DNA sequence

50
Q

Define ‘gene amplification’

A
  • an increase in gene copies by lab methods for research purposes
  • produces enough copies of a gene to allow gene sequencing
51
Q

Define ‘holobiont’

A

host organism and all its symbiotic microbial residents

52
Q

Define ‘metagenomics’

A
  • analysis of genetic info of complex population typically from microbes in environmental or host sample
  • metagenome consists of genomes of many individual microbes
53
Q

Define ‘metatranscriptomics’

A

analysis of active genes and species of microbiome

54
Q

Define ‘microbiome’

A
  • sum of microbes, their genetic info and environment they interact in
55
Q

Define ‘microbiota’

A

all living microbial organisms in the microbiome

56
Q

Define ‘next-generation sequencing’

A
  • umbrella term for number of different modern high throughput sequencing technologies
57
Q

Define ‘operational taxonomic unit’

A
  • grouping of bacterial 16S rRNA sequences by similarity
  • typically grouped at 97% to 99%
58
Q

Define ‘phenotype’

A

observable physical characteristics of organism e.g behaviour or appearance

59
Q

Define ‘phylogenetics’

A

study of evolutionary relationships among groups of organisms

60
Q

Define ‘phylotype’

A

type of bacterium defined by placement in phylogenetic tree on basis of 16S rRNA gene sequence

61
Q

Define ‘species’

A

coherent and distinct groups of bacteria that have been isolated, cultured and named

62
Q

Define ‘symbiosis’

A

two or more species living closely together in long term relationship

63
Q

Difference in core and peripheral microbiome for saliva

A
  • core is the same 13 phyla that is present in everyone
  • peripheral is species present in some and not others
64
Q

Microbiomes of diff individuals form … and these are associated with …

A

clusters
diffs in the metabolome

65
Q

What questions do saliva differences between people raise?

A
  • do the types correlate with disease susceptibility?
  • can they be used as a marker for estimating disease risk?
66
Q

Baacteriophage role in mouth

A
  • control bacterial population in mouth
  • reduce levels of invading pathogens as commensal bacteria have to co-exist with phage and they carry genes between bacteria
67
Q

Do bacteriophage communties vary lots or little between mouth sites?

A

little
- very different between individuals but similar in same mouth
- couples have more similar than twins however

68
Q

2 main types of oral mycobiome

A
  • candida-dominated
  • low-level mixed species
69
Q

Role of acquired enamel pellicle

A

protect enamel

70
Q

Salivary compounds help to control plaque accumulation how?

A
  • aggregate bacteria which are then swallowed
  • antimicrobial effects
71
Q

Salivary molecules that bind to bacteria
What do they do?

A
  • MG2, salivary agglutinin (gp340), PRPs, statherin
  • binds to bacteria and teeth to agglutinate or inhbiit bacteria and exhibit specificity
72
Q

Explain aggregation/agglutination in saliva

A
  • occurs in fluid phase
  • results in large clumps
  • these adhere poorly and are removed with swallowing
73
Q

Explain adhesion in saliva

A
  • proteins in saliva pellicle
  • interaction with bacteria causes adhesion of bacteria to teeth
74
Q

Some proteins exhibit different bacteria binding proporties when in … than when on a …

A

solution
surface

75
Q

Role of immunoglobins in aggregation

A
  • present in saliva
  • agglutinate bacteria (removal by swallowing)
  • secretory IgA (33mg/100ml resting flow, 6mg/100ml stimulated flow)
  • immunoglobins present in gingival fluid (IgG, IgM to activate complement and opsonization)
76
Q

MG2 is a … gene product and secreted by …
It is relatively … and a … (explain)
It binds to …
It’s not/found in pellicle
The non-glycosylated peptide domain can be … - explain

A
  • muc7
  • serous acini of submandibular and sublingual and minor glands
  • small
  • glycoprotein (70% carb, sialyated di-tri-saccharides, lacks ABO blood group determinants)
  • various bacteria inc. streptococcus sanguinis
  • not
  • bactericidal (histamine rich N-term domain can disturb cell membranes)
77
Q

Salivary agglutinin is a … gene product secreted by …
Size?
It’s highly .. and binds to …
It’s identical to … and present in …

A
  • DMBT1
  • all salivary glands
  • 340kDa
  • glycosylated
  • original strep. mutans salivary aggregator
  • gp340
  • pellicle
78
Q

gp340’s role is …

A
  • a glycoprotein in lung washings
  • binds to surfactant protein-D
  • enhances phagocytosis and killing microorganisms by neutrophils and macrophages
79
Q

Explain proline-rich proteins

A
  • can be acidic, basic, glycosylated
  • high concs found in parotid and submandibular saliva (70% of total protein)
  • for calcium phosphate stabilisation
  • C-term is a cryptitope
80
Q

Functional domains of PRPs

A
  • N-term binds to hydroxyapatite
  • C-term binds
  • to actinomyces spp, strep mutans and sanguinis
81
Q

Explain statherin

A
  • low molecular weight
  • secreted by parotid and submandibular gland
  • for calcium phosphate stabilisation with PRPs
  • binds to hydroxyapatite and porphyromonas gingivalis and actinomyces spp
82
Q

Statherin doesn’t bind bacteria when …

A

in soluble state

83
Q

3 broad spectrum antibacterials in saliva

A
  • lysozymes
  • lactoperoxidase/thiocyanate/hydrogen peroxide system
  • lactoferrin
84
Q

Lysozyme effect in saliva

A
  • broad distribution through tears, saliva, sweat
  • not equally effective against all bacteria - oral bacteria more tolerant
  • reduces viability of oral bacteria by cleaving the cell wall peptidoglycan
  • can cause non-enzymatic cell degradation
85
Q

Reactions and role of lactoperoxidase in saliva

A
  • thiocyanate in saliva as KSCN
  • lactoperoxidase is produced by host and bacteria
  • H2O2 is a metabolic by-product of many oral streptococci
  • reaction product is hypothiocyanite plus cyanosulphurous acid and cyanosulphuric acid (all toxic)
  • pK for HOSCN/OSCN is 5.3, more acid favours HOSCN
  • due to uncharged nature, HOSCN penetrates bacterial cell envelope better
86
Q

Role of lactoferrin in saliva

A
  • nearly all life forms have requirement for iron
  • enzyme co-factor
  • lactoferrin binds iron and makes it unavailable
  • some bacteria produce iron-binding proteins called siderophores to compete for host iron
87
Q

Toothbrushing doesn’t eliminate plaque but what kinds of markets can it be specialised to?

A
  • pets
  • dry mouth
  • children
88
Q

Examples of toothpases and their antibacterial enzymes

A
  • Biotene (dual enzyme system)
  • BioXtra (contains lysozyme, lactoperoxidase and lactoferrin)

Microbiology for Dentists (37 decks)

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