8. Refer to the following dilution scheme for question 8 1 rm 1 ml 1 ml 1 ml 9 m

Question

8. Refer to the following dilution scheme for question 8 1 rm 1 ml 1 ml 1 ml 9 ml 9 ml 99 ml 9 ml 1.0 fr eah tuine 4 o Candlbt wre p tdch of i petridishes. The number of colonies (CFUs) counted on each plate are as follows: A. TNTC (Too Numerous to Count) B. TNTC C. 350 D. 34 How many viable organisms per ml. were in the stock solution if dilution C was counted? .If dilution D was counted? A direct count (using a counting chamber) showed that the stock solution contained 4.4 x 106 bacteria per ml. Calculate the percent viability using the direct count and the viable count from dilution D.

Explanation / Answer

a) for dilution C

first, we need to know the dilution factor or how much the original sample is diluted

initially, 1 ml in 9 ml = final volume/sample volume

= 10/1 = 10

3 serial dilutions are :

for the first tube, it contains 9 ml of sterile media now we add 1ml of the undiluted bacterial suspension to yield a total volume of 10ml

1ml/(9ml + 1ml) = 1/10 = 1:10 dilution

for the second tube, it contains 9ml of sterile media now we add 1 ml of the 1:10 diluted bacterial suspension to yield a total volume of 10 ml

1ml/(9ml + 1ml) = 1/10 * 1/10 = 1/100 = 1:100 dilution

for the third tube, it contains 99ml of sterile media now we add 1ml of the 1:100 diluted bacterial suspension to yield a total volume of 100ml

1ml/(99ml + 1ml) = 1/100 * 1/100 = 1/10000 = 1:10000 dilution

total three serial dilution are = 10*100*10000 = 10^7

CFU/ml = (number of colonies * dilution factor)/volume of culture plate

= (350*10^7)/1 = 3.5*10^9

total forming unit = 3.5*10^9

b) for dilution D

for the fourth tube,

1ml/(9ml+1ml) = 1/10 * 1/10000 = 1/100000 = 1:100000 dilution

serial dilution for 4 tubes = 10*100*10000*100000 = 10^12

CFU/ml = (34* 10^12)/1

= 3.4*10^13

c) percent viability can be calculated as = live or viable cell count/total cell count

Related Questions

Navigate

• Browse (All)
• Browse 8
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.