Bacterial cell division 1 Flashcards
Diff types of mutation?
SNPs, subs, deletions, insertions, inversions
Why was the salmonella enterica outbreak in sub saharan africa so devastating?
1 point mutation controlling levels of the virulence factor
Where do insertions usually come from?
HGT
Why is vibrio cholerae so infectious
Phage inserted in its genome–> contains two genes encoding for the cholera toxin
Diff ways to culture bacteria in the lab?
Batch culture, agar plate, continuous culture
Characteristics of batch culture?
No + or - of nutrients/waste
Gas exchange is allowed
Growth conditions change over time
Eventually one or more nutrients become limiting
Characteristics of continuousculture?
Continuous replenishment of growth conditions–> none become limiting
Different types of growth media?
Complex, defined, selective, enrichment, differential
Complex growth media definition ?
Precise chemical composition is not known
e.g. yeast extracts
Defined growth media definition ?
Precise chemical composition is known
No cell products used
Selective growth media definition?
Encourage growth of some organisms while suppressing growth of others
Enrichment growth media definition?
Contains special nutrients that encourages growth of particular organisms that otherwise might not be present in sufficient numbers to allow isolation
Does Not suppress other organisms
Differential growth media definition?
Culture media with a constituent that causes an observable change making it possible to distinguish between different organisms
3 phases of bacterial growth?
Lag, exponential, stationary
Lag phase of bacterial growth?
Time required for cells to adapt to new environment and ready themselves for growth
Re-stocking–>preping 4 growth
Repairing prev damage
Exponential phase of bacterial growth?
Cells growing and dividing as rapidly as possible
Growth rate constant
Cells are most healthy
Rare in nature
OD600 rises exponentially
Stationary phase of bacterial growth?
Growth and division slow
OD600 plateaus
Hibernation state–> metabolic activity slows
What is OD600?
Absorbance to measure number of bacteria
Why does a culture of bacteria enter stationary phase?
Decreasing amounts of nutrients
Death phase of bacterial growth?
One or more essential nutrients completely exhausted or one or more wastes reached lethal toxic levels
Viable count decreases
Could be temp levelling off bc of selection
What is biphasic growth?
exposure to two nutrients. Preferential use of one, which then runs out & then alters its metabolism to make use of the second
One allows them to grow faster than the other
When doing biphasic growth, why is there a plateau between nutrient usage?
For the bacteria to alter their metabolism so they can use the other source
What is generation time?
doubling time–> Time taken for a cell to go through one round of replication and produce identical cells
Why is it difficult to measure bacterial growth when comparing the effectiveness of different antibiotics?
Antibiotics work in diff ways–> some leave the solution cloudy while others dont so absorbance might not work
How is bacterial growth measured?
Viable counts–> colony forming units
Measuring growth by optical density
How to measure colony forming units?
Take samples of cultures at various times
Dilute samples to manageable numbers
Plate them and incubate until colonies can be seen and counted
CFU calculation?
CFU/ml = (# of colonies*dilution factor)/vol of culture plate
Cons of measuring colony forming units?
Cell clumping possible, and needs supportive conditions
Laborious and time consuming
How does measuring optical density work?
MEasure amount of light that is scattered when passed through a culture
Issues with measuring optical density?
Doesnt say how many cells are viable
Needs 10^5-10^6 cells/ml
DIff bacteria have diff light scattering properties
