prokaryotic growth Flashcards
1
Q
binary fission
A
- nucleoid elongates and divides
- membrane folds inward, transverse septum forms
- division of cytoplasm into two daughter cells
2
Q
studying microbes in the lab
A
- provide with nutrients in controlled conditions
- reproducible results
- aseptic technique
- pure cultures mean no interactions
- different behaviour that in natural environment, some studies performed in the field or in mixed cultures
3
Q
requirements for monitoring prokaryotic growth
A
- provide environment for growth
- remove other organisms
- monitoring method sensitive to changes in cell number
4
Q
removing other organisms
A
- using autoclave to pressure cook equipment before organisms to be studies introduced
5
Q
aseptic technique
A
- agar lid and bottles at an angle
- limit time exposed to air
- inoculating loop flame sterilised
6
Q
direct microscopic counts
A
- count number of individual bacterial cells
- counting chamber, plate count
7
Q
counting chamber
A
- grid etched on
- known enclosed volume of suspended bacteria under coverslip
- count cells in certain area of grid to determine concentration of bacteria per ml
- count is irrespective of cell viability, tedious and difficult with small/motile cells
8
Q
plate count
A
- dilute sample (serial dilutions)
- spread on agar plate and incubate at growth temperature
- count colonies grown
- viable count, living cells capable of forming colonies counted, can work out number in original sample
- slow due to incubation time
- countable number of colonies is 30-300, too few is not statistically useful, too many and colonies merge and compete with each other
- use serial dilution to find ideal colony number
9
Q
rapid counting methods
A
- measure factors related to number of cells, not directly counting
- e.g. cloudiness of bacteria in medium, turbidimetric counts using a spectrometer
- the more bacteria, the cloudier, light is scattered more
- monitor growth by change in optical density over time
- real time results
- reduces contamination risks
- easier to do in large samples
10
Q
exponential growth
A
- occurs in perfect conditions
- number of bacteria increase rapidly
- require unlimited resources to continue
11
Q
physical factors affecting bacterial growth
A
- pH
- temperature
- oxygen concentration
- moisture
12
Q
nutritional factors affecting bacterial growth
A
- carbon
- nitrogen
- sulphur
- phosphorous
- trace elements
- sometimes vitamins
- needed to synthesise new individuals
13
Q
bacterial growth curve, lag phase
A
- adaptation to new environment
- no significant increase in number
- cells metabolically active, grow in size, incorporate molecules from medium, produce ATP
14
Q
bacterial growth curve, exponential (log) phase
A
- organisms have adapted to environment
- grow exponentially at genetically determined time interval
15
Q
bacterial growth curve, stationary phase
A
- cell division rate decreases
- usually due to nutrient limitation, sometimes due to build up of toxic products or oxygen limitation
16
Q
generation time
A
genetically determined minimum time between generations of bacteria growing exponentially
17
Q
death phase
A
- less studied
- cells lose ability to divide
- cells die
- total count main remain high, viable count decreases
- some organisms can avoid death phase through spores or dormancy
18
Q
shake flask
A
- mixes in oxygen and keeps cells in suspension in medium
19
Q
complex culture medium
A
- contain a sugar source and amino acids source (usually yeast or meat extracts)
- not specific
- flexible, cheap but variable nutrients so not as reproducible
20
Q
synthetic culture medium
A
- provides exact types and proportions of nutrients organism requires
- requires more knowledge
- more expensive, longer, more steps
- well defined composition so more reproducible
21
Q
natural culture medium
A
- sample or extract of natural substance
- replicates natural environment
- variable
22
Q
selective culture medium
A
- encourages growth of one organisms in a mixed sample
23
Q
differential culture medium
A
- helps distinguish between microbes in a mixed sample
24
Q
MacConkey agar
A
- example of selective and differential medium
- used to spot coliform bacteria e.g. E.coli and other enteric (intestinal) bacteria (gram negative)
- monitor quality of bathing water
- bile salts and crystal violet dye inhbits growth of gram positive bacteria
- E. coli ferments included lactose and colonies colour red
- other gram negative colonies remain white/cream
25
Q
CHROmagar
A
- identification of urinary tract pathogens using differential media
- contains substances that different microbes metabolise, different colonies are different colours
