Microbiology Flashcards
What are the 3 shapes of bacteria
Bacillus (Rod) - Coccus (Sphere) - Spirillum (Spiral)
Obligate aerobes
bacteria that require oxygen to metabolise and carry out cell division
Obligate anaerobes
bacteria that can only metabolise and carry out cell division in the absence of oxygen
Facultative anaerobes
bacteria that can metabolise and divide faster with oxygen present however can grow and divide in the absence of oxygen
What is the purpose of aseptic technique?
- prevent contamination of the environment
- prevent contamination of microbial cultures by unwanted microbes from the environment
Why is all glassware Autoclaved at 121 for 15 minutes?
- to kill any bacteria or spores
Why are petri dish lids opened at a small angle?
- prevent bacteria from entering the petri dish
Why is a roaring blue flame on the bench?
- to create a convection current to uplift air away from the culture
Keeping caps in hand and flaming the neck of the bottle
- to not contaminate the desk or the contents of the bottel
flaming loops until red hot and glass spreaders using ethanol
kill bacteria
in a tube culture experiment where will the types of bacteria be found
- obligate aerobes near the top to absorb maximum oxygen
- facultative anaerobes slightly more near top as divide better in presence of oxygen however found throughout tube
- obligate anaerobes near the bottom of the tube to avoid oxygen
What is a Haemocyometer used for
to measure total cell count
What are the advantages and disadvantages of a viable cell count
Advantages
- counts living cells
Disadvantages
- it is possible to underestimate the population as you cannot be sure each colony has grown from a single bacteria
- takes a long time 24+ hours for bacteria to form colonies
- if a culture is a mix of bacteria with different division rates
What are the advantages and disadvantages of a total cell count
Advantages
- fast (takes only a few minutes)
- can count different cells at the same time
Disadvantages
- difficult to count clumps
- doesn’t discriminate between live or dead cells
- can be difficult to see
What are gram positive bacteria?
have a thick peptidoglycan layer which retains the crystal violet stain (appears purple
What are gram negative bacteria
have a thin peptidoglycan layer and a liposaccharide layer - alcohol will wash crystal violet out counter safranin will stain the cell red
Describe the 5 steps of Gram staining
- heat fix a smear of bacteria
- stain using crystal violet
- fix with iodine
- decolourise with alcohol
- safranin counter-stain
When culturing bacteria what should be present in the nutrient broth or agar
- carbon source, nitrogen source, water source vitamins and mineral salts
- optimum pH and temperature
Describe how to carry out a serial dilution
- use a graduated pipette to transfer 0.1 cm3 into a crew cap bottle along with 9.9 distilled water 10-2
- use a graduated pipette to transfer 0.1cm3 of into screw cap bottle along with 9.9 cm3 distilled water 10-4
- repeat until 10-6
- swirl each bottle to mix gently
How many colonies need to be present to make your selected plates representative
- too few colonies results in inaccurate representation
- too many results inaccuracy with counting
