Question

Y-0.301 6.51-hardts.al 3. A solution containing 100 mL of bacterial broth is subcultured onto 5 plates using the pour-plate method. Each plate receives broth according to the following Table. The Table also lists the results colony counts after 24 hours of incubation. Calculate the number of bacteria per milliliter of the bacterial broth for each of the dilutions. Plate Volume Broth Colonies 331 2 ml 2mix_331 331 Toomi 160 1 ml 0.5 ml 0.1 ml 0.05 ml Colonies/mL 16.62 colonies/m2 1.6 colonies/mL 0.385.com 0,019 cimL 0.002 cimL 1.73 cimi 19 Mean Average: 4. A 10 mL sample of bacterial broth is diluted with 990 mL of sterile broth. One mL of the result is cultured onto a Petri dish of nutrient agar. The next day, 41 colonies are counted on the plate. What is the concentration of bacteria (cells/mL) in the diluted sample? What is the concentration in the original sample? Show all work.

I'm not sure if I completed question 3 correctly. Also, I need help determing question 4.

Answer 1

cfu/ml = (no. of colonies x dilution factor) / volume of culture plate

In experiment 3

There is no dilution done

Hence cfu/ml

= No of colonies/ volume of culture plate

1. 331/2 = 165.5 cfu/ml

2. 160/1 = 160 cfu/ml

3. 77/0.5 =154 cfu/ml

4. 19/0.1 = 190 cfu/ml

5. 4/0.05 = 80 cfu/ml

Average = 150 cfu/ml

4) in the diluted sample cfu/ml = 41

Cfu/ml = 41/1 = 41

5. Concentration in original sample

Dilution factor = 1000/10 = 100

Cfu/ml in original sample = 41*100/1 = 4100 cfu/ml