environmental conditions affecting oral microbiata Flashcards
(75 cards)
1
Q
how do bacteria replicate
A
asexually - binary fission
- circular double stranded dna replicated
- cytoplasm, membrane cell wall divides
- 2 identical daughter cells
2
Q
how do viruses replicate
A
viral replication
- viral particle hijack host cell
- inject its genetic material into the host cell
- allows virus to use host cell cytoplasmic materials to synthesise viral components + replicate its nucleic acid
- then reassembles its various components in the host cells into new viral particles
- new particles release by
a) exocytosis
b) burst out destroying the host cell
3
Q
why do viruses have to hijack host cells
A
- dont possess machinery to synthesise macromolecules
- non-cellular (no phospholipid membrane)
- particles made of nucleic acid (either DNA or RNA NEVER both at same time) enveloped by a protein coating
4
Q
what order of size are viruses compared to bacteria
A
v = NANOmeters (simple microorganisms) b = up to 10 MICROmeters
5
Q
list some microbial eukaryotes
A
fungi
yeast
protozoa
6
Q
how do many oral microbial eukaryotes reproduce
A
asexually
7
Q
how do yeast reproduce
A
BY BUDDING
- form of asexual reproduction
- new organism develops from an outgrowth or bud bc cellular division occurs at a particular site on parent cell
8
Q
we can measure microbial growth by estimating the increase in…
A
cell number cell mass (observing higher dry weight) cellular constituents (ATP + endotoxin)
9
Q
how can we estimate the number of microbes present in a given sample
A
determine total count using
1) total counts (microscopy to count no of cells in surface area and extrapolating number of cells if we know the volume in the sample)
2) viable counts
10
Q
why are viable counts better
A
estimates number of living cells (total count does NOT differentiate between live and dead cells)
11
Q
what is the unit of measurement for viable counts
A
colony forming units
- refers to no of colonies formed on an agar plate following serial dilutions
12
Q
how do total counts work
A
- counting chambers (special glass slides) allows to observe through a microscope + count no of cells present in a chamber + the area of the slide
- then estimate overall no of cells that were in the og sample
13
Q
why do we use viable counts
for example if we had 1ml of saliva
A
- saliva contains 100 million microbes per ml
- if cultured on non-selective medium = surface of agar would be completely covered by bacterial growth after incubation so wouldnt be able to distinguish / count separate colonies
14
Q
what do we do in viable counts
A
- dilute the og sample down in sterile buffer solutions (serial dilutions)
- reduces amount of bacterial cells to a more manageable concentration which are then cultured on agar plates
- with weaker dilutions the number of colonies grown are much easier to count
15
Q
how can we work out the approx. no of cells present in undiluted sample
A
use corresponding dilution factor
number of colonies on plate x reciprocal dilution of same = number of bacteria/ml
16
Q
work out the number of bacteria/ml using a solution diluted 4 times using 1ml of the previous broth each time and finding 32 colonies
A
after 4 transfers of broth we have a dilution of 1:10,000
SO 32 x 10,000 = 320,000 bacteria/ml in sample
17
Q
what do we need to support viral replication and culture viruses
A
living host cells (eukaryotic OR bacterial)
- if use mammalian cells = need tissue culture media to support + maintain growth of host cells which are then infected by the virus you want to culture
18
Q
what are viruses that infect bacteria called
A
BACTERIOPHAGE
19
Q
how can we see if the viral infection of the host in virus cultivation was successful
A
- microscopy
- observe a cytopathic effect (caused by newly formed viral particles when released from the infected host cells)
20
Q
how do we view the cytopathic effect of virus cultivation
A
- microscope
- cell staining
- enables us to view former structures of these damaged cells
21
Q
what food product can be used as a medium to culture viruses
A
eggs
22
Q
what would be the result if we took a sample of plaque or saliva and diluted it down in sterile buffer solution using the serial dilution technique and spread one of the diluted samples on a blood agar plate
A
- after overnight incubation at 37 degreesC
- visible colonies
- colonies that appear identical = likely same organism and species
23
Q
which selective media can be used for gram negative bacteria
A
vancomycin blood agar
designed to attract growth of gram -ves
24
Q
how can we characterise / study the microbial diversity of a sample
A
1) look at colony morphology
2) use differential characteristics (ie cell morphology through gram staining + microscopy)
3) use metabolic activities
4) antigens
5) cellular compositions that are specific + unique to certain microorganisms
6) OR molecular techniques (discussed in previous lecture)
25
what does a typical bacterial growth curve graph layout look like
```
x-axis = time
y-axid = colony forming unit (CFU) - usually as log10 values of the no of bacterial cells determined over time
```
26
which phases can be seen in a bacterial growth curve
a) lag
- no of bacteria remains constant although they are metabolically active
b) log/exponential
- cell numbers increase in logarithmic fashion until it reaches stationary phase
c) stationary
- plateau = cell numbers remain constant before dying off during the death/decline phase
d) death/decline
- cells die off
27
what is seen in a bacterial growth curve under the right conditions
- goes through each phase in turn
28
what happens when conditions are less than ideal for bacterial growth
- growth curve may change slightly
- less or slower exponential growth
- death / decline may take longer to occur
29
which surfaces in the mouth have different biogeography and tissue structures and what does this mean
- mucosal surface
- tongue
- teeth
- enamel surfaces
means all have specific and distinct microbial populations and there is variation of microbial composition at various sites
30
when else may there be variation in microbial composition
at different times of day
- after tooth brushing
- after meals
31
what determines the presence of certain microbial species at different sites
their ability to invade or tolerate host defence molecules and metabolise nutrients present in the local environment
32
which factors effect the survival and prevalence of bacteria mostly oral bacteria
1) Host defences
2) Availability of nutrients
3) Temperature
4) Oxygen / redox potential
5) pH
6) Antimicrobial compounds
33
what happens when microbes are high in numbers
start to modify local environment
| like all populations/communities
34
effect of temperature on microbial growth:
| what are the different categories of microbes and their specific optimum growth rates (temp grow best at)
1) PSYCHROPHILES = 20 degreesC
2) MESOPHILES = 35 degreesC
3) THERMOPHILES 65 degreesC
35
what are extremophiles
- thrive at extreme environmental conditions (ie hydrothermal vent near volcano)
36
what is the temperature of the mouth
a) in heath
b) in inflammation
a) 35 degreesC
| b) temp at inflamed site rises to 39 degreesC
37
what is the consequence of the rise in temperature resulting from inflammation
- effect on local microbial populations
- alters gene expression
- leads to different phenotype of their metabolic functions
38
what are obligate aerobes
require presence of O2 to survive / thrive (atmospheric O2 level)
39
what are facultative anaerobes / aerobes
don't mind if O2 is present or not
40
what are microaerophiles
require some level of atmospheric O2 to survive
41
what are aerotolerant anaerobes
prefer the absence of O2 to survive
BUT
are tolerant to minute levels of O2
42
what are obligate anaerobes
require the absolute absence of O2
- highly sensitive to O2
- able to generate energy without recourse to molecular oxygen
- require sites with low redox potential in the mouth
43
where would the aerobic and anaerobic microbes be found in a container filled with a medium and with a gradient of o2 where o2 conc is highest at the top where the lid is (air at lid = atmospheric O2)
obligate aerobes = at top near lid
facultative anaerobes / aerobes = everywhere in container but mostly at the top
microaerophiles = just below level of obligate aerobes (grow in sub-atmospheric O2 levels)
aerotolerant anaerobes = at the bottom
obligate anaerobes = not present in container as there would still be small amnt of O2 at bottom
44
what type of aerobe/anaerobe are the majority of organisms in the mouth and where are these mainly found
facultative anaerobes OR obligate anaerobes
- dental plaque
- subgingival pockets
- deep in biofilms
45
what are the derivatives of molecular oxygen and how do these contrast it
singlet oxygen
peroxide anion
superoxide anion
hydroxyl free radical
- molecular oxygen is NOT toxic but its derivatives are (they are chemically reactive)
46
what do derivatives of molecular oxygen derive from
biproducts of cellular metabolism
47
what are derivates of O2 and what can they cause but how can this be opposed
strong oxidising agents
cell death
but some bacteria excrete enzymes to process and neutralise or detoxify these reactive o2 molecules (detoxifying enzyme)
48
what happens when o2 and reactive o2 species are too high in number
oxidation of important enzymes essential to the functioning of the bacterial cells
obligate anaerobes eventually die
49
what are some examples of detoxifying enzymes (convert toxic reactive o2 molecules into less toxic molecules) and their actions
1) superoxide dismutase (superoxide ion -> H2O2 + O2)
2) catalase (2H2O2 -> 2H2O + O2)
3) peroxidase (H2O2 -> 2H2O) = requires NADH + H+
50
what is the redox / oxidation-reduction potential (Eh)
measure of the tendency of a solution/chemical compound to acquire electrons and therefore be reduced or give electrons and be oxidised
measured in volts or millivolts
51
what occurs in redox through oxidation
get high value of redox potential
| higher it gets = higher tendency to gain electrons thus be reduced
52
what is the Eh (redox potential) of
a) fresh bacterial medium
b) bacterial medium following anaerobic growth
a) +100 to +200mV
| b) less than -100mV
53
what is the Eh (redox potential) of
a) gingival crevice in health
b) in gingivitis
a) +73mV
| b) -48mV
54
what is the Eh (redox potential)
a) before plaque
b) 7 days into plaque development
a) +200mV
| b) -141mV
55
why does the redox potential decrease in disease cases
- change in local conditions
| - ie increased temperature due to inflammation
56
why is it important to note that although o2 concs are linked to redox potential the factors are both independently contributing to the distribution of microbes in the oral cavity
in an environment where O2 is absent
could still have a high redox potential
in this case strict anaerobes cannot grow
57
effect of pH on microbial growth:
| what are the different categories of microbes and their specific optimum growth rates (pH grow best at)
1) ACIDOPHILES = prefer acidic
2) NEUTROPHILES = prefer neutral pH
3) ALKALOPHILES = prefer alkaline pH
58
what is the pH of saliva in health
6.75 - 7.25
59
what are ACIDURIC organisms
survive and grow at low pH
60
what is the pathway for the bacterial metabolism of glucose
```
glucose
-> (via glycolysis)
pyruvate
->
1) acetate, formate, ethanol
or
2) lactate
```
61
how does substrate concentration influence metabolism in bacterial metabolism of glucose
what does this illustrate
if carbs are in excess
- homofermentation occurs
- lactate produced
if carbs are limited
- heterofermentation occurs
- acetate, formate and ethanol are produced
illustrates there are various strategies employed by bacteria to survive and produce energy with whats available around them (evolved these to survive)
62
what happens when endogenous mucin and exogenous sucrose are metabolised by bacteria
production of acid and drop in pH
mucin = slow rate of acid production + small fall in pH
sucrose = rapid rate + low terminal pH (pH<5)
63
what happens when endogenous GCF is metabolised by bacteria
- rise in pH
- from pH 6.90 to 7.25-7.50
- due to use of gcf components ie proteins and glycoproteins whos metabolic activity gives rise to ammonia (alkaline - NH3)
64
what happens if the changes in pH made by endo and exo genous nutrients are not reversed
- gradient in pH drive shift in microbial population (those who dont like new conditions move away/die and those who thrive colonise)
- metabolic activity of first colonisers changes this microenvironment condition
65
what is resting pH in dental plaque
- neutrality
- favours
1) S. sanguinis,
2) Actinomyces naeslundii 3) Neisseria etc
66
what is low pH in dental plaque
- favours aciduric species
1) S. mutans
2) Lactobacilli
- the 2 above thrive in presence of strong acids + are acidogenic (produce strong acids themselves)
- their presence usually inhibits “health-associated” species
67
what is high pH in dental plaque
- promotes growth of some anaerobes
1) Porphyromonas gingivalis -- survives by its metabolic activity of proteins - usually in subgingival pockets
- is implicated in periodontal disease SO seen in high abundance in periodontitis and can drive pH up to 7.5
68
what do we need knowledge of to control microorganisms
and HOW would we try and control them
- microbial physiology and growth
- their ecology and population dynamics within microbial communities
- use external chemicals and physical agents (ie antibiotics BUT - antibiotic resistance)
69
what other strategies can be used to control the growth and abundance of bacteria
1) good oral hygiene
2) mouthwash and toothpaste containing antimicrobial compounds (ie chlorhexidine, triclosan, metal salts, essential oils)
3) fluoride
4) immunisation (active / passive)
5) replacement therapy
6) probiotics
70
why is fluoride important to prevent/inhibit microorganisms
- inhibits acid production
| - especially effects streptococci species
71
why is immunisation important to prevent/inhibit microorganisms
- build up of immunity against infection by microorganisms ie Streptococcus mutans anti-caries
- production of sufficient antibodies allows faster reaction of protection during 2nd infection
72
what is replacement therapy used to prevent/inhibit microorganisms
- therapeutic intervention
| - replace microorganisms (ie know pathogen) with less pathogenic one in the resident microbiota
73
why are probiotics important to prevent/inhibit microorganisms despite controversy surrounding them
- aim to maintain a healthy balance of good+bad bacteria in gut
- ie some dairy products containing live cultures of bacteria
- some are being developed for the oral microbiota in case of S. salivarius
74
what method is important to prevent/inhibit microorganisms within a clinical setting and how is this done
cross infection control
1) STERILISATION= complete removal/destruction of all organisms (autoclave; oven)
2) DISINFECTION = kills most viable organisms (chemical: hypochlorite)
3) PASTEURISATION = pathogens, reduces microbial load
75
give an example of a bacteria which thrives at neutral / resting pH
actinomyces naeslundi
