September 25

Question 1

Microscopic Count

Answer 1

Count cells directly on a slide with a calibrated grid

Limitations: cannot distinguish living cells (can be stained to distinguish), overlook small cells, low density cultures/ samples hard to count, motile cells must be immobilized, debri/ artifacts mistaken for cells

Question 2

Viable Cell Count

Answer 2

Plate count (pour or spread)

Trying to dilute original sample to the point where 30-300 CFUs on a late

Question 3

Peptone Blank

Answer 3

Isotonic solution, prevents cell damage

Has a nutrient source, so if it is turbid it was contaminated

Question 4

MPN

Answer 4

Most Probable Number Method

Used when you expect a low number of cells (such as water quality tests)

Question 5

Turbidity

Answer 5

Cells scatter light passing through suspension, the more cells the more turbid

Question 6

Microbial mass

Answer 6

Allows you to come up with a growth curve

Spectrometer to measure turbidity

More turbid=more microbial mass

Problems: cells can clump, makes it look less turbid

biofilm formation

Cant differentiate living from dead cells

Question 7

Photospectrometer

Answer 7

Measures the amount of light transmitted or absorbed through sample

Question 8

Minimum Growth Temperature

Answer 8

Chemical reactions are slow

Metabolism slows

Transport slows

Enzymes slow

Low growth rate

Firm (gel) cell membrane (transport accross membrane slows)

Question 9

Optimum Temperature

Answer 9

Highest growth rate

Max enzyme function