Week 3 material Flashcards
(46 cards)
What is a gram stain used for?
To differentiate between 2 types of bacteria
What is the cell membrane structure of gram positive + gram negative
Gram positive
- Has multiple peptidoglycan layers
- Is thick and rigid
Gram negative
- Has one peptidoglycan layer in between his outer and cytoplasmic membrane
- It is flexible, porous, and helps with regulating osmosis of the cell
Where do gram positive and gram negative bacteria live
GP: lives in external environments such as the skin
GN: lives in watery + moist environments such as the GI tract or GU tract, catheters or IV lines
which bacteria can NOT be gram stained
- bacteria with NO cell wall
- bacteria that exists inside of a host cell
- bacteria not large enough to be seen with a light microscope
what methods can we use to identify the organism that has caused a disease?
- mass spectroscopy using MALDI-TOF
- PCR - molecular based methods
- biochemicals/table top tests
what is MALDI-TOF
- a type of mass spectroscopy method
- laser is used to ionize protein molecules which come from bacterial isolate (pure culture of the bacteria)
- the now ionized molecules get put through a vacuum + the speed they travel at through the vacuum depends on its protein’s mass to charge ratio
- the different speeds of the molecules are presented on to a screen
- the speeds are unique to a species which can help identify the organism or the species of the organism
what are the limitations of MALDI-TOF + what is another method we can use
some species have a similar or the same spectra (they travel at the same speed) - this also means the species are very closely related and MALDI-TOF can not differentiate between the different species
another method to be used is the biochemicals or molecular based tests
what does the biochemical method look for
bile solubility
- is the bacteria soluble in the bile or not
when do we used molecular based methods or PCR
when we’re looking for a specific bacteria
- can be SINGLEPLEX (1 pathogen) or MULTIPLEX (more than 1 pathogen that can cause the disease)
what is susceptibility testing and what do they look for
it’s a test to see if a drug works against the pathogen
done in vitro - they put a bug and a specific concentration in a tube and look at the growth of the bug
they are looking for the lowest concentration of drug that can stop the pathogen from growing - this is call the MINIMUM INHIBITORY CONCENTRATION (MIC)
what are the 3 AST (antimicrobial susceptibility testing) methods in the clinical micro lab
- broth microdilution
- gradient strip diffusion
- disk diffusion
what is broth microdilution
tests the pathogen against serial dilutions of the drug over time
serial dilution = a series of dilutions with a gradual decrease in concentration (in this case the concentration of the drug)
this is the most used AST method
it can be either a manual or automated method
the MIC is shown where the concentration has visibly stopped the bug’s growth - dark gray in this case or clear tube
what is gradient diffusion
uses antimicrobial-impregnated strip (strip contains the antimicrobial drug) with a graded concentration (high to low concentration of drug) the strip then gets placed on a agar plate w/ bacteria
the different concentrations cause a symmetrical elliptical growth
the MIC is seen where the ellipse meets the strip
aka E-test
a manual method
what is disk diffusion
uses a circular disk with a fixed concentration of the drug
gets put with a fixed amount of the bug overnight
measures the diameter of the area of growth inhibition
large enough = the bacteria is susceptible to this drug/drug works against the bacteria
too small = the bacteria is resistant to the drug
manual method
aka kirby-bauer (KB) method
how are results interpreted
they look at a a lot of clinical data on the treatment outcomes of drugs that have been against pathogens
the bug-drug combination determines if the pathogen is susceptible or resistant to the drug
when the outcome is good for that combo at physiological dosing (the amount your body would naturally or normally produce) then the bacteria is susceptible
when the outcome is bad for the combo at physiological dosing, then the bacteria is resistant to the drug
what is selective reporting
when the most relevant antibiotics are reported to providers
it would be the safest + most effective drug for the patient, sample/body, and space
depends on the availability of the drug in the hospital, province, or country
it’s a way to implement safer practice - although there are exceptions in individual cases where they may need to use something more intense
when are some antibiotics not reported
if it is not used during pregnancy - they do not get reported in samples from the BC Women’s hospital patients
some antibiotics are last resort when dealing with pathogens that are resistant to multiple drugs - if a pathogen is susceptible to other drugs, it does not get reported
some drugs do not penetrate or get into the specific tissue or site the sample is from
how do you apply koch’s postulates to a virus
- you have to identify a gene that causes for the virus to be pathogenic or virulent
- this gene can encode for a virulence factor
Example
- Hemagglutinin is a gene that is present in the pathogenic strain of influenza and codes for surface proteins
- it helps the influenza virus to attach to the host cell and enter it
- it gets attacked by the immune system
- if the influenza is mutated, it’s HA gene is not functional which makes the influenza not as virulent
- if we restore the HA gene’s function, then the influenza is virulent again and pathogenic
how do antibiotics lose effectiveness
when bacteria goes through RANDOM mutations which gives them resistance and is then naturally selected for because they’re the ones who survive
what are the requirements for a bacteria to grow
- needs a source of energy
Example: sugars + fatty acids - metal ions
Example: iron - optimal environment
temperature
pH
oxygen or a lack of oxygen
what are extremophiles
microorganisms such as bacteria that can survive in harsh conditions (extreme pH or temperature)
what conditions do most microorganisms grow in
In moderate conditions
Temperature = mid-range temperatures (called mesophilics)
pH = neutral pH
Oxygen or lack of oxygen:
- some microorganisms are obligate aerobes - they require oxygen + perform aerobic respiration
- some are obligate anaerobes - can’t survive in oxygen + perform fermentation
- other microorganisms are aerotolerant anaerobes + facultative anaerobes - they’re somewhere in between the two
what is the bacterial growth curve and which phase is the best for antibiotics to attack
1. Lag phase = NO increase in number of living bacteria
2. Log phase = exponential increase in number of living bacteria
- actively dividing via binary fission
- this phase is the best for antibiotics to target b/ this is where a lot of the bacteria is in the middle of being created + antibiotics can ruin this process - specifically antibiotics that target the synthesis of DNA, cell wall, and proteins
3. Stationary phase = number of living and dead bacteria is the same, there is no increase or decrease to the amount of living bacteria, the amount is staying the same
- nutrients get used up and waste products accumulate
- the synthesis of nucleic acids, proteins, and peptidoglycans slow down which also makes them less susceptible to antibiotics
- in this phase - bacteria may go into survival mode by creating virulence factors or endospores
4. Death or Decline phase = exponential decrease in number of living bacteria
examples of physical methods of microbial control
microwaving food/heat
salt for drying out food
smoking food
fermentation of food
copper cookware
preserve bodies
pasteurization
refrigeration
altering the acidity
desiccation (removal of moisture)
- add solutes (salt or sugar)
- solutes draw water from area of low solute concentration (inside the cell) to high concentration (outside of cell)
- cells can NOT tolerate the high osmotic pressure conditions and will die
