environmental conditions affecting oral microbiata Flashcards
how do bacteria replicate
asexually - binary fission
- circular double stranded dna replicated
- cytoplasm, membrane cell wall divides
- 2 identical daughter cells
how do viruses replicate
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
why do viruses have to hijack host cells
- 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
what order of size are viruses compared to bacteria
v = NANOmeters (simple microorganisms) b = up to 10 MICROmeters
list some microbial eukaryotes
fungi
yeast
protozoa
how do many oral microbial eukaryotes reproduce
asexually
how do yeast reproduce
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
we can measure microbial growth by estimating the increase in…
cell number cell mass (observing higher dry weight) cellular constituents (ATP + endotoxin)
how can we estimate the number of microbes present in a given sample
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
why are viable counts better
estimates number of living cells (total count does NOT differentiate between live and dead cells)
what is the unit of measurement for viable counts
colony forming units
- refers to no of colonies formed on an agar plate following serial dilutions
how do total counts work
- 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
why do we use viable counts
for example if we had 1ml of saliva
- 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
what do we do in viable counts
- 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
how can we work out the approx. no of cells present in undiluted sample
use corresponding dilution factor
number of colonies on plate x reciprocal dilution of same = number of bacteria/ml
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
after 4 transfers of broth we have a dilution of 1:10,000
SO 32 x 10,000 = 320,000 bacteria/ml in sample
what do we need to support viral replication and culture viruses
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
what are viruses that infect bacteria called
BACTERIOPHAGE
how can we see if the viral infection of the host in virus cultivation was successful
- microscopy
- observe a cytopathic effect (caused by newly formed viral particles when released from the infected host cells)
how do we view the cytopathic effect of virus cultivation
- microscope
- cell staining
- enables us to view former structures of these damaged cells
what food product can be used as a medium to culture viruses
eggs
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
- after overnight incubation at 37 degreesC
- visible colonies
- colonies that appear identical = likely same organism and species
which selective media can be used for gram negative bacteria
vancomycin blood agar
designed to attract growth of gram -ves
how can we characterise / study the microbial diversity of a sample
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)
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
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
what is seen in a bacterial growth curve under the right conditions
- goes through each phase in turn
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
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
when else may there be variation in microbial composition
at different times of day
- after tooth brushing
- after meals