Standard Plate Count Worksheet

Standard Plate Count Worksheet

Read each question carefully and answer to the best of your ability. Show all calculations where necessary.

1. What is the primary purpose of performing a Standard Plate Count (SPC)?

2. Which of the following is NOT a common dilution factor used in SPC?

1. The acceptable range for colony counts on a plate for SPC is typically between   and   colonies.

2. Serial dilutions are performed to reduce the bacterial concentration to a countable range, preventing   plates.

3. After inoculation, petri dishes are incubated at an optimal temperature for bacterial growth, usually around  °C.

1. Explain why 'colony-forming units' (CFU) are used instead of 'number of cells' when reporting SPC results.

2. Describe the potential sources of error in a Standard Plate Count experiment.

A microbiologist performs a Standard Plate Count on a water sample. They take 1 mL of the sample and perform a series of 1:10 dilutions. After plating 0.1 mL from the 10^-5 dilution onto an agar plate, they count 45 colonies after incubation.

1. Calculate the original concentration of bacteria in the water sample (CFU/mL). Show your work.

1. The pour plate method is generally preferred over the spread plate method for heat-sensitive microorganisms.

2. All bacteria present in a sample will grow and form colonies on a standard agar plate.