Module 3

Question 1

Binary Fission

Answer 1

Cell contents doubled and cell elongates
Cellular membrane folds in middle
Cell wall forms in middle and 2 cells are separated

Question 2

Generation Time

Answer 2

time required for binary fission to take place (to double population)
Rapid bacteria and optimum conditions = 15-20min
In Lab times usually faster than in vivo as there are no defence mechanisms in place

Question 3

Generation Time factors (3)

Answer 3

Genetic control
Available nutrients
Environmental conditions

Question 4

In Vivo

Answer 4

in the human body

Question 5

In Vitro

Answer 5

In the laboratory

Question 6

Viable Bacterial Count

Answer 6

counts only viable/live bacteria

Determined by their ability to reproduce (only accurate way is to perform a colony count)

Question 7

Total Bacterial Count

Answer 7

counts both viable and dead bacteria

Question 8

Colony Count

Answer 8

Bacterial suspension is added to molten agar and poured into a plate. After incubation, each colony = 1 viable bacterium
10 colonies = 10 “Colony forming units” = 10 CFU/mL

Question 9

Total Bacterial Count methods (5)

Answer 9

Microscope (use measured chamber)
Electron Particle Counter (hard due to size of bacteria)
Visual Turbidity Measurement (McFarland Standards)
Spectrometer
Nephelometry

Question 10

McFarland Standard

Answer 10

Measures turbidity of a broth culture (degree of cloudiness) against a standard set of turbidity values.
Made by varying amounts of 1% sulfuric acid and 1.175 aqueous solution of barium chloride. This results in white precipitate of barium sulphate.

McFarland Standard tube # 0.5
BaCl2 mL: 0.05
H2SO4mL: 9.95
Bacteria/mL x 10^8: 1.5

Multiply across Tube #, BaCl2, bacteria/mL.
H2SO4 decreases by 0.05/ 0.5 increase in tube #

Question 11

Spectrophotometer

Answer 11

Light passed through bacterial suspension and measured. Amount of light passing through is related to how much bacteria is in the suspension.
Result in T% which has to be converted into a number by using standard plate count methods

Question 12

Nephelometer

Answer 12

Instrument that actually measures amount of light scattered by bacteria in suspension.

Question 13

Lag Phase

Answer 13

No increase in cells
Cells gathering nutrients
Cells begin to divide

Question 14

Log Phase

Answer 14

Cells actively dividing 
Clear medium becomes cloudy
Colonies start to form on plates
Good cellular morphology, easy to differentiate gram +/-
Bacteria most likely to show motility
Bacteria susceptible to antimicrobials

Question 15

Stationary Phase

Answer 15

Total number of viable cells remains constant because of
a) all cells stop dividing
or
b) growth rate = death rate
Easy to find spores, not a good demonstration of motility
Gram pos may stain gram neg

Question 16

Death Phase

Answer 16

Viable cell decline
Presence and production of spores may maintain viable cells for longer
Gram positive may stain negative
Morphologies often not typical
Best time to find spores
May not demonstrate motility

Question 17

Batch Culture

Answer 17

A culture that goes through the lag, log, stationary, death growth phases.

Question 18

Chemostat

Answer 18

Allows continual supply of fresh medium and air into growth chamber to encourage bacteria to stay in log phase