(12)

Question 1

member of Enterobacteriaceae that ferments lactose within production of gas within 48 hours at 37 degrees a Celsius

Answer 1

coliforms

Question 2

a series of dilutions used to reduce the concentration of a culture and thereby produce between 30 and 300 colonies when plated, providing a means of calculating the original concentration; reduces cell density to achieve countable plates

Answer 2

serial dilution

Question 3

a means of keeping track of how much of the original sample is still present after the dilution

Answer 3

dilution factor

Question 4

the cell or group of cells that produces a colony when transferred to plated media

Answer 4

colony-forming unit (CFU)

Question 5

What is considered a “countable” plate?

Answer 5

Between 30 and 300 individual colonies

Question 6

What is the outcome of diluting samples?

Answer 6

• It systemically reduces cell density, thereby producing at least one dilution that will yield countable plates
• It provides a mathematical framework by which to link the unknown (original cell density) with the known (number of colonies on the plate).

Question 7

What is the dilution factor of 1-ml added to 99-ml water? 1-ml added to 9-ml? 0.1-ml added to 0.9-ml?

Answer 7

10^-2 because it now is only 1/100 of its original concentration

Question 8

Be able to determine the original density of bacteria using the following calculation:

Answer 8

CFU/mL = # of colonies counted

volume plated x dilution factor