✅3.4 -microbiology Flashcards
Give 3 ways that you could distinguish between types of bacteria in a school lab
Shape
Size
Staining characteristics
Name 3 ways microbiologists could classify bacteria
Metabolic features
Antigenic features
Genetic features
What are metabolic features?
The chemical reactions that occur in bacteria
What are antigenic features
The proteins on/sticking out of the surface marker of the protein
What are genetic features of bacteria
Difference in DNA and base sequences in DNA
What 2 names can be given to the chemical whose 3D mesh gives the bacterial cell wall it’s structure
Peptidoglycan and Murein
Does Gram positive and gram negative have a peptidoglycan layer?
Gram positive: thick layer of peptidoglycan
Gram negative: thin layer of peptidoglycan (not exposed)
Does Gram positive and gram negative have lipopolysaccharide?
Gram positive: no
Gram negative: yes, covers the peptidoglycan layer
Name steps 1&2 of gram staining for both + and -
1) crystal violet, all cells take up dye on outer layer
2) treat cells with iodine, all cells stay purple
Describe step 3 of gram staining for both + and - bacteria
3) decolorisation with alcohol
Gram positive: the alcohol does not affect the stain so it remains purple
Gram negative: the alcohol dissolves the lipopolypolysaccharide layer which is stained,
As the layer dissolved the dye is removed (colourless)
Describe step 4 of gram staining for both + and - bacteria
4) counter stain with safranin
Gram positive: the dye does not affect the purple stain as already stained purple
Gram negative: the peptidoglycan layer, now exposed is dyed red by safranin
Why is gram negative bacteria harder to treat with antibiotics
Additional level on gram (lipopolysaccharide level) makes it harder to kill as extra protection.
What 5 conditions are needed to culture bacteria in a lab
- Water presence
- Suitable temperature
- Suitable nutrients (glucose and nitrogen)
- Suitable pH
- Suitable oxygen levels
List 3 types of nutrients that are necessary for bacterial growth
1) glucose
2) nitrogen (building amino acids)
3) vitamins and mineral salts
Define Obligate aerobe
Microorganisms that must have oxygen to carry out their chemical reactions. These organisms will die in the absence of oxygen.
Define obligate anaerobe
Microorganisms do not need oxygen to carry out their chemical reactions. These organisms will die in the presence of oxygen
Define facultative anaerobe
Microorganisms that respire aerobically but can respire anaerobically in the presence of oxygen
Define aseptic
Conditions that aim to exclude the presence of unwanted microorganisms
Give 2 reasons why we use aseptic technique during the microbiology experiments
To prevent contamination by the microbes being handled
To prevent contamination of microbial cultures by unwanted microbes from the environment
Name the 2 ways equipment can be steralised prior to microbiology experiments
Heat
Irradiation= heat labile (stable) plastics as many melt
Describe aseptic steps that you could take to ensure there’s no bacteria there to start
- sterile Petri dish with irradiated heat liable
- sterile equipment in an autoclave 121 degrees for 15 minutes
- bleach work surface
- wash hands
How do you minimise entry if unwanted bacteria to Petri dish
Only open Petri dish a small amount for a limited time
Why do you incubate bacteria culture in a school lab at 25 degrees
To stop human pathogens growing as human bacteria/pathogens grow at 37 degrees
What is the total count of bacteria
Total count counts both living and dead bacteria (over estimate)
What is the viable count of bacteria
Viable counts only living bacteria (underestimate)
What do you need to do to count bacteria
What assumptions do you make?
You must count using serial dilution
Assumption: one cell gives rise to one colony, this can create an underestimate if bacteria due to possible clumping
What 3 things do you need to know to estimate total number of bacteria
- Colony number
- Dilution factor
- Volume of sample
How do you pick which colony number to used
Pic the highest value of countable non clumped colonies
How do you calculate dilution factor
Total volume in the tube/volume added to the tube
What are the 2 most commonly used dilution factors
x10 and x100
How do you calculate the multiplication value
1/sample volume
Equation to estimate the value of bacteria in the original sample
Colony number x dilution factor x sample volume multiplication factor
Name the 3 types of bacteria
Coccus (circular)
Bacillus (cylindrical)
Spirillum (spiral)
Name the 4 stages in the population growth graph
Lag phase
Log phase
Stationary phase
Death phase
Why is there a low rate of population growth in the first 3 hours of the experiment
Take time for the digestive enzymes to be produced, nutrients to be digested, protein synthesis to occur and genes for the production of specific enzymes to be switched on/ off.
