Module 3: Bacterial Reproduction and Growth Curves Flashcards
Define generation time
Time required for binary fission to take place and bacterial population to double
What factors affect generation time?
Genetic control (DNA) Available nutrients (some metabolized faster than others [glucose=fast, proteins=slow]) Environmental conditions (temperature, oxygen, carbon dioxide)
Is generation time faster or slower in vivo?
Slower due to a number of factors that slow bacterial growth
What are the 2 types of bacterial counts?
Viable count - live bacteria
Total count - live and dead bacteria
How is the viable bacteria count determined?
By demonstrating their ability to reproduce
Colony count by adding bacteria to molten agar and letting harden, each colony = 1 viable bacteria
How is a total bacteria count determined?
Under microscope - counting all bacteria in a ruled chamber
Visual turbidity - cloudiness of broth = number of bacteria (compared against McFarland standards)
How are McFarland standards prepared?
Varying amounts of 1% sulfuric acid to varying amounts of 1.175% aqueous barium chloride creating a white precipitate
What is the amount of bacteria compared to a 0.5 McFarland standard?
1.5 x 10^8 bacteria/mL
What instruments can measure bacterial counts in solution?
Spectrophotometer and nephelometer
How does spectrophotometry measure bacterial counts in solution?
Turbidity is measured at either %T (transmittance) or optical density
Calibration curves convert value to number of bacteria/mL
How does nephelometry measure bacterial counts in solution?
Measures the amount of light scattered
What are the 4 phases of the bacterial growth curve?
- Lag phase
- Logarithmic or Exponential phase
- Stationary phase
- Death phase
What happens in the lag phase of the growth curve?
Little to no cell number increase, cells are metabolizing enzymes and getting larger
How can the lag phase be shortened?
Take inoculum from bacteria already in the log phase (actively growing)
Use a medium most suitable for the bacteria to allow it to adjust more quickly
What happens in the log/exponential phase of the growth curve?
All cells are dividing at a constant rate
Liquid medium becomes cloudy, colonies start appearing on plates
Why is the log phase most desirable for working with bacteria?
Best cellular morphology
Most likely time to show motility
Most susceptible to antibiotics
Why might the log phase of growth end?
Exhaustion of nutrients
Build up of toxins
What happens in the stationary phase of the growth curve?
Number of viable cells remains constant, cells stop dividing, growth rate equals death rate
Why might the stationary phase be of use in the lab?
Easier to find spores as they start growing at the end of the log phase
What happens in the death/decline phase of the growth curve?
Viable cells decline and dye exponentially
Broth may clear due to autolysis
Why is the death phase important in lab?
Gram stains are poor
Involution morphology is most likely
May not be motile
Best time to find spores
Bacteria that are able to form colonies on solid medium after overnight incubation have a generation time of about
a. one hour
b. twenty minutes
c. four hours
d. ten hours
b. twenty minues
Which of the following methods gives an accurate viable count?
a. nephelometry
b. electronic particle counter
c. colony count
d. turbidity measurements
c. colony count
When the growth rate equals the death rate, the culture is in the
a. lag phase
b. log phase
c. stationary phase
d. death phase
c. stationary phase
Spores are not usually found in the
a. lag phase
b. log phase
c. stationary phase
d. death phase
a. lag phase
Bacteria are most susceptible to antibiotics in the
a. lag phase
b. log phase
c. stationary phase
d. death phase
b. log phase
Cultures for microscopic examination for motility should be in the
a. lag phase
b. log phase
c. stationary phase
d. death phase
b. log phase
0.1 mL of urine is added to approximately 20mL of molten agar, mixed well, and poured into a petri dish. Inspection of the plate the following day showed 86 small white bacterial colonies and 24 large yellow colonies.
a. What is the total colony count in CFU/L (SI units)?
b. What is the colony count of the large yellow colonies in SI units?
c. Is this a viable or total colony count?
a. 1.1 x 10^6 CFU/L
110 colonies/0.1mL x 1000mL/L = 1100000
b. 2.4x10^5 CFU/L
24/0.1mL x 1000mL/L = 240000
c. viable
