Module 3 Flashcards
What is generation time?
The time it takes for binary fission to occur or the population to double.
What factors affect generation time?
Genetic control, available nutrients, environmental conditions.
Are generation times greater in vivo or in vitro?
In vivo
What type of bacteria does a viable count account for?
Only live bacteria.
What must be used for a viable count?
A colony count. Suspension is added to agar and incubated, every colony corresponds to one bacterium.
What type of bacteria do total counts account for?
Both living and dead.
What are the different ways to perform a total count?
Count under the microscope
Electron particle counters
Visual turbidity
What standards does visual turbidity use?
MacFarland standards
What are the components of MacFarland standards?
Barium chloride and sulfuric acid
What are the ratios of the MacFarland standards?
For tube 0.5, 1, 2, 3:
BaCl2- 0.05, 0.1, 0.2, 0.3
H2SO4- 9.95, 9.9, 9.8, 9.7
Bacteria (x10^8)- 1.5, 3, 6, 9
What does spectrophotometery measure and how does it do this?
It measures turbidity of bacterial suspensions. It registers the amount of light transmitted (not absorbed) by bacteria. The more bacteria, the less light is measured.
What does nephelometery measure?
The amount of light scattered by bacteria.
When can spectrophotometery and nephelometery counts be considered viable?
In log growth phase.
What are the phases of the bacterial growth curve and their characteristics?
Lag- little/no cell no. increase
Log- cells divide at a constant rate
Stationary- no increase or decrease
Decline- cell no. declines exponentially
When is the best time to find spores?
Death/decline phase
When is the best time to work with bacteria?
Log/exponential phase
When are bacteria most susceptible to antibiotics?
Log/exponential phase
How can you shorten the lag phase?
Take bacteria from culture actively growing in log phase
Choosing suitable medium
Why does the number of bacteria stop increasing in the stationary phase?
Cells stop dividing (nutrient depletion)
Growth rate is the same as the death rate
How can culture be maintained at log phase?
Using a chemostat (removes gas and old media, supplies fresh media and nutrients)
How do bacteria reproduce?
Binary fission
