Please please help and please how your work! Thank you!! 1. You need to create a
ID: 196827 • Letter: P
Question
Please please help and please how your work! Thank you!!
1. You need to create a solution containing a total of 0.10 mg glucose. You have a stock solution of glucose at a concentration of 250 ug/ml. How many ml of the stock solution do you need?
2. You are asked to determine how many colony forming units are found in 100 grams of soil. You begin by mixing 1 gram of the soil into water, totaling 100 ml in volume. Then you remove 1 ml of this solution and mix it in 99 ml of sterile water. After repeating this serial dilution 2 more times, you plate (in triplicate) 0.1 ml of the final dilution. After incubation, you observe 142, 173, and 180 colonies on the three different plates. How many CFU are present in the 100 grams of soil?
3. You were given a 1 liter flask containing bacteria with the concentration of 4.6 x 1010 CFU/ml. Devise a dilution scheme that will result in an allowable number of colonies on each of two plates.
Explanation / Answer
1.
Concentration of the stock = 250 ug/mL
Required amount of glucose = 0.1 mg = 100 ug
1 mL -----> 250 ug
? mL ------> 100 ug
= 100/250
= 0.4 mL
= 400 uL
2.
Solution I = 1 g soil ----> 100 mL (Dilution = 100 times)
Solution II = 1 mL of solution I + 99 mL water (Total dilution = 100 X 100 times)
Solution III = 1 mL of solution II + 99 mL water (Total dilution = 100 X 100 X 100 times)
Solution IV = 1 mL of solution III + 99 mL water (Total dilution = 100 X 100 X 100 X 100 times)
Volume of solution IV used for plating = 0.1 mL
Average number of colonies = (142+173+180)/3 = 165 colonies
0.1 mL of solution IV = 165 colonies
1 mL solution IV = 1650 colonies
1 mL of solution I = 1650 X 10^6 colonies
For 100 g of soil = 1650 X 10^8 colonies
= 1.65 X 10^11 colonies
3.
Concentration of bacteria = 4.6 X 10^10 CFU/mL
Allowable number of colonies = 115 - 150 CFU/mL
Dilution I = 1 mL stock + 99 mL media (Dilution = 100 times)
Dilution II = 1 mL dilution I + 99 mL media (Dilution = 10000 times)
Dilution III = 1 mL dilution II + 99 mL media (Dilution = 1000000 times)
Dilution IV = 1 mL dilution II + 99 mL media (Dilution = 100000000 times)
Concentration of Dilution IV = 460 CFU/mL
1 mL of dilution IV + 3 mL of media = Dilution V
Concentration of Dilution V = 460/4 CFU/mL
= 115 CFU/mL