Name __________________________________________ Section _____________
Bacterial Enumeration - Results & Interpretation – 15 pts total
Use the results provided in the file "Enumeration of Bacteria in a Culture using the Techniques of Serial Dilution
and the Spread Plate Method - RESULTS" to complete this assignment.
7 pts for table. ** If the plate is TFTC or TMTC/TNTC you must record that in the table, don’t just
put a dash or leave blank.
Quantitative Techniques – Questions – 8 pts
1. You plated 0.1 ml of a 10-3 dilution an E. coli culture. After incubating for 48 hours at 37°C there
are 63 colonies on the plate. How many CFU were in the original culture? (1 pt)
PLATE Tube
dilution Volume
Plated
Final dilution
on the plate
(0.5 pt each space)
Number of
colonies
(0.5 pt each space)
CFU/ml
(0.5 pt each space)
1 10-4 0.1 ml
2 10-5 0.1 ml
3 10-6 0.1 ml
4 10-7 0.1 ml
Average -
only average the
countable plates
(1 pt)
SU23
10^-5 dilution
TMTC
N/A
10^-6 dilution
TMTC
N/A
10^-7 dilution
139 colonies
1.39 * 10^9 CFU/mL
10^-8 dilution
TFTC (28
colonies)
N/A
Alexa Campanella
63 / (10^-3 * 0.1) =
630,000 CFU
