Question

Bacteria #2 is a Bacteria #3 is a III. Calculation: (1) Serial dilution: (3 pts/each) 1. 0.2 mL of sample is added to 0.8 mL of diluent, what is the Dilution? 2. 0.01 mL of sample is added to 0.99 mL of diluent, what is the Dilution? :100 mL 0.2 mL of a sample was added to 0.8 mL of a diluent. Then, 0.1 mL of this first dilution was added to 0.4 mL of a diluent. What is the total final dilution? (Show your calculations!) 3. (2) Calculate the number of bacteria per mL: (3 pts) You transfer 0.1 mL bacteria with 1:100,000 of dilution into an agar plate. After two days of growth, the agar plate has 236 colonies. What is the number of bacteria per mL, from the original culture? 0000): 23600,000 mレ

Answer 1

Answer. 1. For calculating serial dilution

Sample added/ total volume (diluent +sample)

Sample = 0.2ml and diluent= 0.8 ml total volume = 1.0 ml

0.2/1.0 = 1/5

Hence dilution is 1/5 or 1:5

Answer 2. Given sample =0.01 and diluent =0.99 then dilution = 0.01/1.0= 1/100 or 1:100

Answer 3.dilution of first = 0.2/1.0 = 1/5

Dilution of second = 1/5. × 0.1/0.5 = 1/25 or 1:25 dilution.

Answer 2 number of colonies in original sample = number of colonies × dilution factor / sample volume

Here number of colonies = 236

Dilution = 100000

Sample volume = 0.1

Then original concentration of cell =(236×100000)/0.1 = 236000000 cells.