6.4.7 microorganism cultures Flashcards
1
Q
2 types of growth mediums used for microorganisms
A
- broth - kept in bottles/tubes
- agar - melted & poured into petri dishes
2
Q
what does typical nutrient agar contain
A
- peptones
- yeast extract
- salts
- water
- may contain glucose/blood
3
Q
standard 6-step procedure of aseptic techniques
A
- wash hands
- disinfect working area
- have bunsen burner nearby to heat air = causes air to rise which prevents air-borne microorganisms settling & creates area of sterile air
- pass neck of bottle over flame once opened/when closing to prevent bacteria entering bottle
- don’t lift lid of petri dish off completely - only open enough to introduce desired microorganism
- glassware/metal equipment passed through flame before/after contact with desired microorganisms
4
Q
3 main steps involved when growing microorganisms on agar plates
A
- sterilisation
- inoculation
- incubation
5
Q
how is the nutrient agar medium sterilised
A
- heating autoclave at 121 degrees for 15 minutes
- kills all living organisms eg. bacteria, fungal spores
- when medium cooled sufficiently, it’s poured into sterile petri dishes & left to set
- lid kept on petri dish to prevent infection
6
Q
different ways of inoculation
A
- streaking = wire inoculating loop transfers drop of liquid medium onto surface of agar & drawn into streak
- seeding = sterile pipette transfers small drop of liquid medium onto surface of agar/petri dish before agar poured in
- spreading = sterile glass spreader used to spread inoculated drop over agar surface
- small cotton swab/bud moistened with distilled water & collects microorganisms from surface to carefully wipe over agar medium
7
Q
how is the petri dish incubated
A
- label & tape top to bottom using 2 strips of adhesive tape (don’t seal dish completely)
- placed in suitable warm environment eg. incubator
- placed upside down = prevents condensation falling onto agar & agar drying out too quickly
- temperatures depend on organism being grown
8
Q
define closed culture
A
population where all conditions set at start & no exchange with external environment
9
Q
4 stages of closed culture growth curve
A
- lag phase
- exponential phase
- stationary phase
- dead/decline phase
10
Q
describe the lag phase
A
- population doesn’t grow quickly
- population is small/adjusting to environement
- may involve: taking up water, cell growth, activating genes, synthesising specific proteins (enzymes) etc.
11
Q
describe the log (exponential phase)
A
- organisms adjusted
- have enzymes needed
- all have sufficient nutrients/space to grow rapidly & reproduce
- population doubles in size with every generation (some microorganisms this is once every 20-30 minutes)
12
Q
describe the stationary phase
A
- increasing numbers of microorganisms eventually use up nutrients & produce increasing waste products (eg. carbon dioxide, other metabolites)
- rate of population growth declines & number of individuals dying increases until rate of reproduction equals death rate
- no population growth
13
Q
describe the death phase
A
- nutrients run out
- concentration of waste products may become lethal
- more organsims die than being produced = population begins to fall
- eventually all organisms die
14
Q
when are primary metabolites made
A
produced during normal activities of microorganism & collected from fermenter during log phase
15
Q
when are secondary metabolites made
A
- produced in stationary phase
- population must be kept in close culture & metabolites can be collected at end of stationary phase/during decline phase
