3. Bacterial Reproduction and Growth Curves Flashcards
What factors affect generation time?
Genetic control determined by chromosome
Available nutrients
Environmental conditions
What is the difference between in vivo and in vitro?
In vivo - in the human body
In vitro - in the laboratory
What is the difference between viable counts and total counts?
Viable counts - only viable or live bacteria (only accurate way of determining this is to perform a colony count)
Total counts - both viable and dead bacteria
What is a colony count?
An accurate way of measuring a viable count
Mix a measured amount of bacterial suspension and add to molten agar. This is then put in a petri plate to solidify and incubated. Bacterial colonies are then counted and each colony corresponds to one viable bacterium.
What are the McFarland standards? What is it used for?
Is a series of turbidity standards Prepared by adding 1% sulfuric acid and 1.175% aqueous barium chloride which results in a white precipitate
Used for counting both viable and dead bacteria though a visual turbidity measurement (degree of cloudiness) which is directly related to # of bacteria
What is the McFarland standard for a 0.5 tube?
Tube # 0.5
BaCl2 mL 0.05
H2SO4 mL 9.95
Bacteria/mL x 10^8 1.5
0.5 McFarland standard = 1.5 x 10^8
What is a spectrophotometer?
A way to measure the turbidity of a bacterial suspension using optical density.
If the scattered light does not reach the detector, the more bacteria and the less light is measured.
Measures bacteria per mL
What is Nephelometry?
An instrument that actually measures the amount of light scattered by bacteria in suspension
Describe the bacterial growth curve.
- Lag Phase
- Log Phase
- Stationary Phase
- Death Phase
What occurs in the lag phase of bacterial growth?
Little or no increase in the number of cells
Cells are actively metabolizing enzymes or other macromolecules as they adjust and prepare for division
Cells get larger
What occurs in the log phase of bacterial growth?
All cells are dividing at a constant rate (logarithmic)
Each time a cell division takes place the number of bacteria doubles
Indicated by a clear liquid medium turning cloudy, or colonies start to form while on solid media
What is the importance of working with cultures in the log phase?
Good cellular morphology
Easy to differentiate between Gram pos and Gram neg bacteria
Most likely to show motility
Most susceptible to antimicrobials
What occurs in the stationary phase of bacterial growth?
This stage starts when cells stop dividing at a constant rate.
The total number of viable cells remains constant by one of two activities taking place : all cells stop dividing or growth rate = death rate.
Easy to find spores in this phase.
What occurs in the death phase of bacterial growth?
Number of cells decline in an exponential fashion
Gram stains are poor
Best time to find spores
Define generation time.
Is the time required for binary fission to take place and for the bacterial population to double.
