Topic 6.1- Bacteria and disease Flashcards
(42 cards)
Why are aseptic techniques important when culturing microorganisms?
to produce uncontaminated culture so results are reliable + repeatable
List the basic aseptic techniques
- wipe surfaces with antibacterial wipes/cleaner
- set up Bunsen burner nearby. Convention currents prevent microbes from entering culture
- flame inoculating loop + neck of bottles before use
- minimise time that vessels containing bacteria are open
- sterilise all equipment e.g. using an autoclave
- wear protective clothing
Outline how to culture microorganisms
- Transfer bacteria to agar plate using sterile inoculating loop or pipette
- Tape lid on at 2 ends then invert the dish and incubate. In school labs ensure that dish isn’t airtight + do not incubate above 25 degrees to avoid growth of pathogen
Explain the difference between a streak plate and a spread plate
- streak plate: aims to obtain single colonies by rotating the plate to build layers of the culture on at least 3 separate streaks
- spread plate: aims to distribute microorganisms evenly with a sterile spreader
Describe the 3 types of nutrient medium
-liquid broth
-solid agar
(usually contain nitrogen, carbon, + minerals, often enriched with protein from extract of yeast, blood or meat)
-selective mediums (contain highly specific nutrient balance, only certain microorganisms grow)
Give the advantages of using a broth medium
- can provide anoxic + oxic conditions depending on depth, which helps to identify microbes/ determine their optimum conditions
- can grow a very large quantity of bacteria
Give the advantage of using agar as the medium
can obtain single, discrete pure colony for study
Name the 4 phases of the bacterial growth curve
- lag phase
- log phase
- stationary phase
- death phase
What happens during the lag phase?
microorganisms need to adjust to the environment before reproducing so population size only increases slowly
What happens during the log phase?
after every round of division population size doubles (exponential growth)
What happens during the stationary phase?
reproduction rate= death rate, so population size stabilises at its max
What happens during the death phase?
microorganisms die due to build up of toxic waste products + lack of nutrients
Name 3 methods used to estimate the growth of a bacterial culture
- cell count
- turbidity measurement (type of colorimetry to measure opacity)
- dilution plating
Explain how to conduct a cell count
- dilute broth sample with equal volume of trypan blue to stain dead cells blue
- use a calibrated haemocytometer with volume 0.1mm3. Count the cells in each of the sets of squares and calculate the mean
- number of bacterial cells = counted number x10^4 per cm3
Suggest advantages and disadvantages of using a cell count
advantage: only counts living cells
disadvantages:
- slow
- expensive equipment
- large margin for human error
Explain how to conduct a turbidity measurement
- use colorimetry. measure absorbance or % transmission of samples with known microorganism count
- plot calibration curve: absorbance/ % transmission (y-axis) number of microorganisms (x-axis)
- record absorbance/ % transmission of unknown sample
Suggest advantages and disadvantages of using a turbidity measurement
advantages:
-quick
-can be conducted in the field
disadvantages:
-counts both living and dead cells
-requires calibration curve from known samples
-assumes equal density of cells across culture
Explain how to conduct dilution plating
- grow a colony from a single microorganism
- perform serial dilution with distilled to see single colonies
- prepare a lawn plate and count colonies
- number of cells= number of colonies x dilution factor
What are endotoxins?
lipopolysaccharides that are an integral part of the outer layer of the cell wall of Gram-negative player
What are exotoxins?
soluble proteins that are produced and released into the body by bacteria as they metabolise and reproduce in the cells of their host
Define lipopolysaccharides
large molecules containing a lipid element and a polysaccharide element
What is tuberculosis?
a lung disease caused by Mycobacterium tuberculosis and M.bovis
What’s the primary infection of tuberculosis?
the initial stage of tuberculosis when M.tuberculosis has been inhaled into the lungs, invaded the cells of the lungs and multiplies slowly, showing no obvious symptoms
What is a tubercle?
the result of a healthy immune response to an infection by M.tuberculosis. a localised inflammatory response forms a mass of tissue containing dead bacteria and macrophages
