Module 3 Flashcards
(18 cards)
Generation time
The time it takes for the bacterial population to double
The time it takes for binary fission to take place
Factors that can affect the generation time
Genetic control
Available nutrients
Environmental conditions
How do bacteria normally reproduce?
Binary fission
Viable counts
Counts only live bacteria
Colony count
Only accurate way to determine viable count
Measured amount of bacterial suspension added to molten agar, poured into petri plate, solidified, incubated
Each colony = one viable bacterium
Total count under microscope
Ruled chamber with measured volume of bacterial suspension
Difficult due to small size of bacteria
Total count by electronic particle counters
Similar to blood cell counters
Difficult due to small size of bacteria
McFarland standards
Used to determine total counts by visual turbidity
Various amounts of 1% sulfuric acid and 1.175% aqueous barium chloride
White precipitate of barium sulfate
Bacteria that are able to form colonies on solid medium after overnight incubation have a generation time of about:
20 minutes
Which method gives an accurate viable count?
Colony count
Spores are not usually found in which phase of the bacterial growth curve?
Lag phase
Bacteria are most susceptible to antibiotics in which phase on the growth curve?
Log phase
How are McFarland standards prepared?
Adding varying amounts of 1% sulfuric acid to varying amounts of 1.175% aqueous solution of barium chloride. This results in a white precipitate of barium sulfate.
0.5 McFarland standard
1.5 x 10^8 bacteria/mL
Lag phase
Little or no increase in the number of cells
Actively metabolizing enzymes and other macromolecules
Log phase
Cells dividing at a constant rate
Benefits: Good morphology, motility, most susceptible to antimicrobials
Stationary phase
Total number of viable cells constand
All cells stop dividing or growth rate = death rate
Not good to demonstrate motility, Gram + may stain Gram -
Easy to find spores
Death/decline phase
Exponential decline of viable cells Gram + may stain Gram - Atypical morphologies, involution forms May not demonstrate motility Best time to find spores
