9.1, 9.2-9.5, 13.2 Flashcards
What is the most common form of bacterial reproduction?
Binary Fission
What are the 4 steps of Binary Fission?
- Growth of cell size and increase in cell components
- Replication of DNA
- Division of cytoplasm (cytokinesis)
- Septum formation and division of daughter cells
What is cytokineses direct by?
FtsZ protein
What assembles to form divisome?
FtsZ assembles Z ring to form divisome
What does a divisome do?
Activates production of peptidoglycan and septum
What does is the term called when referring to the time it takes to double population?
Generation Time (Doubling Time)
How long is the generation time for E. Coli?
20 minutes
How long is the generation time for B. subtilis?
120 minutes
What is the generation time for S. Aureus?
30 minutes
What is the generation time for M. Tuberculosis?
15-20 hours
What is this equation used for?
Nn= N02^n
Calculating the population size
What does the Nn represent in Nn= N02^n?
Number of cells at generation n
What does N0 represent in Nn= N02^n?
Initial number of cells
What does ^n represent in Nn= N02^n?
number of generations
What is culture density?
of cells/unit vol.
Which step of the growth curve has the inoculum cells added and adjust to culture medium; no change in population?
1st step: Lag phase
Which step of the growth curve has binary fission occurring; cell replication > cell death
2nd step: Log (exponential) phase
Which step of the growth curve has resources becoming depleted; cell replication = cell death
Step 3: Stationary phase
Which step of the growth curve has endospores forming; cell replication < cell death
Step 4: Death Phase
What occurs during Lag phase?
- Cells grows larger; metabolically active
- Damaged or shocked cells undergo repair
- Initial cell numbers do not change
What are some factors that determines the duration of the lag phase?
Genetic make-up
Media composition
Initial inoculum size
How is generation time determined?
Genetically determined; intrinsic growth rate
_____ vs____ is exponential
Time vs # of cells is exponential
At what point of the growth curve are the microbes most susceptible to disinfectants and antibiotics that affect protein, DNA, and cell-wall synthesis?
Log (exponential phase)
- this is because they are more focused in growing/expanding rather than repairing
What happens during log phase?
Constant growth and uniform metabolism
What happens during stationary phase?
Waste accumulates; nutrients gradually used up
Culture density is constant
Undergo sporulation
At which point of the growth curve do cells’ synthesis slows; less susceptible to antibiotics; expression of virulence factors and secondary metabolites?
Stationary phase
At which phase of the growth curve has toxic waste accumulating; nutrients exhausted
Death Phase
Why and when do cells lyse and release nutrients
During death phase; to help surviving cells and endospore-formers
What are surviving cells with slow metabolism called? What are some characteristics of them?
Persisters
Chronic infections (tuberculosis) and antibiotic resistance
What type of system culture has infinite resources; nutrients and air are replenished; dead cells and waste are removed? What is an example of this system?
Open system cultures
Chemostat
What method of quantifying populations size has cells counted under a microscope?
Direct microscopic cell count
What is a flaw when using direct microscopic cell count?
It cannot distinguish live vs dead
When using the direct microscopic cell count method, what is the calibrated slide where we put our known volume called?
Petroff-Hausser chamber
What method of quantifying populations size has cells counted under a microscope or flow cytometer and has a red stain bind to damage cells for indication?
Fluorescence Staining
What method of quantifying population size detects electrical resistance change due to cell density (as fluid that contains particles/cells is drawn through the micro-channels, each particle causes a brief change to the electrical resistance of the liquid?
Coulter counter
Is there a flaw when using Coulter counter?
Yes, it doesn’t differentiate live/dead
What method of quantifying populations size is a count of viable cells; samples are diluted and grown on solid media
Viable Plate counts
How are the results of viable plate counts expressed?
Colony forming units per volume (CFU/ml)
What is the countable range in a viable plate count? What is it when it’s TFTC and TNTC?
30-300 CFU/ml
<30 - TFTC (too few to count)
>300 - TNTC (too numerous to count)
What method is used to measure growth when the sample is very dilute and may not contain enough microbes for plate count?
Membrane filtration technique
What does the membrane filtration technique do?
Known vol. filtered through a membrane; membrane plated and colonies counted
What does most probable number (MPN) mean?
Statistical method used when counts are very low ( <30 CFU/ml)
What happens during the method of MPN?
Uses 3 log dilutions grown in 3-5 replicates
Growth is determined positive or negative
Pattern is compared to reference table
What is turbidity?
optical density (describes a material’s ability to absorb the power of a given light)
What is turbidity measured with?
Spectrophotometer