microbiology part 1 Flashcards
to review the microbial aetiology of caries and provide context for preventative approach objectives: revisit properties of dental biofilm review the methods to characterise the oral microbiome assess the evidence for the role of micro-organisms in caries describe the main causative bacteria define the properties of cariogenic bacteria
what are dental biofilms
they are natural and beneficial
how many species are present in the dental biofilm
700+ species
what is the biofilm composed of
bacteria
viruses
fungi
what does the biome help with
with key functions
helps to regulate the immune system
and helps with host defences
what is desquamination
the shedding of epithelial cells- reduces the bacterial load
examples of non shedding surfaces
teeth
dentures
implants
what is the bacterial load like on non shedding surfaces
it is high unless you remove the load by eg brushing
how can we tell which bacteria are beneficial or harmful
by traditional culture such as
grow the organism
what are the issues with traditional culture
laborious
expensive
only half the species in the mouth grow on blood agar
very time consuming- need to do multiple tests and isolate the species
what are the issues with microscopy
only will tell you the shape of the species( cell morphology)
what does FISH stand for
fluorescent in situ hybridisation- can help recognise a few species
what are the molecular approaches to identify the species in the microbiome
HOMIM (human oral microbiome identification microarray )
DNA-DNA hybridisation
PCR
high throughput whole genome sequencing
what is the gold standard to see what species an organism is
high throughput whole genome sequencing- and put into the database and you can see which organism is present
what is metagenomics
complex clinical sample such as plaque
extract DNA
cut DNA
sequence and then the short fragments will make a long sequence
tested across a database and we can see which species are present
what does metatranscriptonomics look at
RNA to see which proteins are transcribed
what is HOMD
human oral microbiome database
how is the bacteria in the dental biofilm organised
structurally organised
functionally organised
why are bacteria in the biofilm functionally organised
so that the aerobic organisms are nearer the surface for O2
and anaerobic at the base
what are the features of the dental biofilms
concerted and collaborative metabolism food chains environment modification matrix formation cell-cell signalling complex interactions- balance
why are dental biofilms helpful
they help get rid of harmful organisms in the mouth due to pathogen exclusion
how can the load of helpful bacteria in the dental biofilm be reduced
due to long term antibiotic therapy
what can be the result of long term antibiotic therapy
overgrowth of yeasts
bacteria from which organ can cause a inflammatory reaction
gut and the mouth but rare
eg Crohns disease in the gut
why do we rarely see inflammatory reaction in the mouth
because the bacteria communicate between one another and the host
what is the entero salivary nitrate circulating system
where nitrate from green vegetables is reabsorbed from the gut and appears in saliva and the beneficial bacteria can break it down to nitrite which modifies blood pressure . and nitrite that is swallowed becomes acidified nitric oxide which is antibacterial and stimulates mucus
where does the body get nitrate from
from green veggies we eat
what does the nitrate get converted to
get converted into nitrite by beneficial bacteria in the oral cavity
why is nitrite good
it can reduce blood pressure
what does XS nitrite that is swallowed get converted into
acidified nitric oxide
where is the XS nitrite converted
in the stomach
why is acidified nitric oxide good
due to the fact it stimulates mucus production which protects the stomach lining and it is antibacterial
examples of bacteria seen in carious lesions
strep mutans
lactobacillus
other acidogenic/tolerating bacteria
which bacteria are seen in health
strep oralis/mitis fusobacterium nucleatum actinomycetes spp haemophillus spp neisseria spp
why is caries multifactorial
as it has many components such as:
susceptible host
environmental factor
key oral organisms
what factors are included in environmental factors
cariogenic diet
poor oral hygiene
low saliva flow rate
what happens to older peoples flow rate of saliva
decreases- side effect if medication eg blood pressure medication
what factors are including in confounding factors
fluoride availability
diverse natural microbiota
non specific virulence traits
what is the evidence that microbes are involved in the aetiology of dental caries
gnotobiotic( known life) animal studies:artificial conditions where they are not exposed to organisms
and then micro-organisms are introduced and we see the effect
gnotobiotic animal studies showed
specificity of certain microrganisms- eg lactobacilli causes caries
diet- we do not have caries if fermentable sugars are not present
transmission- from infected animal to non infected
antim
antimicrobial agents- effective antimicrobials prevent caries
why ca we not do germ free ethical studies on humans
due to ethical reasons
what is a cross sectional study
where we take a group of people- at one time point
sample of plaque and analyse for which species and see where caries is or isn’t
what is the issue with cross sectional studies
cheap but only show associations- do not know certainly if the bacteria found in the lesion caused the lesion or grew as a consequence of the lesion
what is a longitudinal studies
small group of people- caries free
choose caries prone site
a % of those people should develop caries in that area in a few years
monitor every 3-6 months for several years
compare the microorganisms before during and after
what are the disadvantages of longitudinal studies
expensive
takes a lot of time- not many done
Vaccination
Vaccination against strep mutans in rodents and primates
Why are vaccinations for varies not introduced to humans
There were a few side effects and the public confidence in vaccines was little so the cost of clinical trials
But fluoride was having an effect
Vaccine hasn’t been tested in human clinical trials
what serotype is found of strep mutans
c
e
f
what serotype is found of strep srobinus
d
g
what species of actinomyces is present
a naeslundii
a odontolyticus
a isrealii
what species of bifidobacteria
bifidobacterium
which species of candida is found
c albicans
describe strep mutans
gram +ve cocci
found on hard surfaces- non shedding surfaces
implicated in initiation of caries
describe lactobacillus
gram +ve rods
implicated in advanced dental caries
describe bifidobacterium ( more recent years)
gram +ve rods
branched cells
recently implicated caries
what are the difficulties with trying to associate microorganisms with dental caries
disease occurs at sights where there is natural biome
difficult to correlate microbiota to enamel status
lesions can remineralise
pathogenic traits are relatively non specific
multifactorial nature of caries
what bacteria is found at caries sites
strep mutans but not always
in both proportions and isolation frequencies
which bacterias have an inverse relationship
between strep mutans and strep sanguinis
what % of caries had more than 10% MS
71%
what percentage of caries free fissures had no detectable MS
70%
when does MS first start to show
early demineralisation
can caries also occur if MS is not present
YES
examples of acidogenic bacteria
strep mitis
strep oralis
give examples of lactate utilising bacteria
veillonella
what is lactate converted to
propionate or acetate
describe veillonella
gram negative coccus
anaerobic
utilises lactic acid in plaque
name base generating species
s salivarius will make the pH basic when urea is present
s sanguinis will make the pH basic when arginine is present
a naeslundii will make the pH basic when urea is present
when will s salivarius make the ph basic
when urea is available
when will s sanguinis make the ph basic
when arginine is present
when a naeslundii will make the ph basic
when urea is available
which species is found in people with low caries or no caries
strep dentisani
strep A12
what do both strep dentisani and strep A12 do
they are arginolytic meaning they break down arginine into ammonia snd inhibits strep mutans
what can strep dentisani and strep A12 be used as
As probiotic
describe the urea to ammonia conversion
urea + h20—–> ammonia + CO2 by the enzyme urease
describe the arginine deiminase system
arginine—->citulline+ ammonia—-> ornithine + carbamyl- P—-> ATP+ C02 + ammonia
what bacteria is associated with childhood caries/nursing bottle caries
mutans streptococci
lactobacilli
which bacteria is associated with root surface caries in early studies
actinomyces spp
which bacteria is associated with root surface caries in later studies
MS
lactobacilli
which bacteria is associated with root surface caries in recent studies
diverse microbiota
actinomyces spp- A israelii and A gerensceriae
MS
gram negative rods
what bacteria do you find in infected dentine
MS
lactobacilli
actinomyces spp- A israelii and A gerensceriae
gram negative anaerobic rods - prevotella
what molecular changes do you find in infected dentine
strep mutans
eubacterium saburreum
diverse array of lactobacillius
diverse array of prevotella
what else is found in infected dentine
acidogenic bacteria
combined with proteolytic and collagenolytic bacteria
characteristic of cariogenic bacteria
rapid sugar transport and acid production PEP-PTS
aciduricity
EPS
IPS
