e analyzed a water sample by spread-plate. The results are shown below. Which di
ID: 257310 • Letter: E
Question
e analyzed a water sample by spread-plate. The results are shown below. Which dilution would you use to calculate the number of bacteria in the original sample? (3 pts) Plate # Dilution 10 10-3 104 10-5 TNTC 250 28 TNTC 264 20 TNTC 238 18 The dilution that should be used- What is the number of bacteria in the original sample? 2. A water sample is diluted to 103 and 1 ml of this dilution is inoculated into a pour plate. After 24 hours 120 colonies are counted. Therefore, the number of bacteria per ml of the original sample is reported to be: (2 pts) a) 120 b) 120,000 c) 12,000 d) 1,200 e) there is not enough information to derive an answer pread 3. Show how you would dilute a water sample and plate a 104 dilution using the S Plate technique. Be sure to include all essential information. I will not fill in any missing values. (4 pts)Explanation / Answer
1. 10^-3 dilution is a good sample for calculating the concentration.
It gave an average (264+250+238)/3 = 250.6 CFU/mL.
Original concentration = 250.6 X 10^3 = 2.506 X 10^5 CFU/mL
2. Option B is correct.
Number of CFU for 10^-3 dilution = 120
Original concentration = 120 X 10^3 = 1.2 X 10^5 CFU/mL
3. To obtain 10^-4 dilution,
1 mL of undiluted sample + 9 mL water = 10^-1 dilution: Dilution I
1 mL of dilution-I + 9 mL water = 10^-2 dilution: Dilution II
1 mL of dilution-II + 9 mL water = 10^-3 dilution: Dilution III
1 mL of dilution-III + 9 mL water = 10^-4 dilution: Dilution IV
4. Option A is correct.
Only viable cells form a colony. A single colony is a derivative of a single bacterial cell.
5.
Undiluted sample volume = 5 mL
Dilution I (A) = 5 mL of undiluted sample + 45 mL = 10^-1 dilution
Dilution II (B) = 1 mL of A + 99 mL = 10^-2 dilution; Total dilution = 10^-3
Dilution III (C) = 1 mL of B + 99 mL = 10^-2 dilution; Total dilution = 10^-5
Final number of colonies per 0.1 mL = 135
Final number of colonies per 1 mL = 1350
Original concentration = 1350 X 10^5 CFU/5 mL
= 2.7 X 10^7 CFU/mL
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.