Determine the cfu/g of soil | Homework Help

20 g soil sample was aIDed to 80 ml of water to make the final volume of 100 ml (tube A). Then, 10 ml of the ‘tube A’ solution was taken and aIDed to 90 ml of water (tube B). 1 ml of the ‘tube B’ solution was taken and aIDed to 9 ml of water (tube C). 1 ml of the ‘tube C’ solution was taken and aIDed to 99 ml of water (tube D). 10 ml of the ‘tube D’ solution was taken and aIDed to 90 ml of water (tube E). Now, 0.1 ml out of the tube C, D or E was taken and plated on agar-media plates in triplicate. The table below shows colony numbers counted, after overnight incubation.

C

D

E

TNTC (too numerous to count), 431, 378

43, 52, 33

1, 0, 6

(a) What are the fold dilutions in the tubes C, D and E against the tube A?

(b) Determine the CFU/g of soil.

(c) How many bacteria were present in 8 g of soil?