CSIM 1.36 Bacterial Growth and Cultivation Flashcards
How many mitotic divisions is needed from one cell to reach 32000 bacteria?
Log2(32000) = roughly 15
UNDER OPTIMAL CONDITIONS
What are the phases of the bacterial colony growth curve?
- Lag phase
- Exponential/log phase
- Stationary phase
- Death phase
IMG 93
Describe the lag phase of the bacterial growth curve
‘Shock’ period
• Cell is synthesising new components to deal with new environment
• Varies in length
Describe the log phase of bacterial growth
- Population is most uniform in terms of chemical and physical properties
- Rate of divisions is constant
- Cells most vulnerable to antibiotics in this phase (because the cells are producing more cell walls)
Formulate an equation linking generations, initial number of cells and final number of cells
N = N₀ x 2ⁿ
Where:
• N = final colony size
• N₀ = initial colony size
• n = number of generations
Formulate an equation linking generation time (g) to duration of exponential growth (t) and number of generations.
g = t/n
Where:
• g = generation time
• t = duration of exponential growth
• n = number of generations
Formulate an equation that represents the log phase line mathematically (IMG 94)
Combine this equation with the one linking generation time (g) to duration of exponential growth (t) and number of generations.
SLOPE = Log(2) * n/t SLOPE = 0.301 * n/t
g=t/n
Therefore:
g = 0.301/SLOPE
How can the number of bacteria be counted using serial dilution?
Serial Dilution:
• Take 1 ml of the solution and add to 9ml of broth to make a 1:10 solution and add 1ml of this to a petri dish
• Take 1ml of this solution and add to another 9ml broth to make a 1:100 solution and add 1ml of this to a second petri dish
• Repeat several times for 1:1000, 1:10000, 1:100000
• Select the petri dish with as many colonies as possible, but with none of those colonies touching
• Each colony originates from one bacterium
• Multiply the number of colonies by the ratio of the solution placed onto that petri dish to calculate the number of COLONY-FORMING bacteria per ml of the original solution
IMG 95
How can the number of bacteria be counted without using serial dilution?
Microscopy haemocytometer:
• A grid which only permits one bacterium per grid square is observed under a microscope
• The bacteria in a certain area is counted and the number of bacteria is extrapolated
• Limitation: cannot differentiate between live and dead bacteria
Turbidity
• Measure the optical density of the bacteria
• Measure the light that shines through a solution of the bacteria
Describe the stationary phase
Limiting factor of colony size is reached due to too many toxins or insufficient nutrients
• Death rate = reproduction rate either because reproduction slows or death rate rises
Describe the death phase
Describe the population that results from the death phase
Cells die and an exponential rate
Highly-resistant organisms
Describe why antibiotic treatment must always be completed
To avoid proliferation of highly-resistant organisms resulting in antibiotic resistance
IMG 96
Describe the pH which is optimum for:
1) Acidophiles
2) Neutrophiles
3) Alkalophiles
1) 1 - 5.5
2) 5.5 - 7
3) 8.5 - 11.5
What is the pH of:
1) Stomach
2) SI
3) LI
1) 2
2) 4-5
3) 7
How many bacteria are found in:
1) Stomach
2) SI
3) LI
1) Almost bacteria-free
2) Very small number of bacteria
3) Large numbers (90% of the weight of faeces)
