After this lab you should be able to:
- Perform a serial dilution on a bacterial culture.
- Design a dilution scheme for a Standard Plate Count.
- Determine the final dilutions in a serial dilution and the # of CFU/ml (cell density) of the original sample.
- Utilize the Spectrophotometer to determine the OD of bacterial culture samples.
- Graph absorbance vs. the dilution of your serial dilutions.
- Compare and contrast Direct Count, Standard Plate Count, and the Indirect Turbidimetric method of enumeration bacterial counts in a sample.
Why do we want to know how many bacteria are in a sample or specimen? Do you think it’s important to know the number of microbes in food? Quantifying the bacterial level in a sample can be done in several ways. New rapid diagnostic tests can help identify particular bacteria in a sample, but the total count is informative in a manufacturing or diagnostic process.
What about in human disease? Typically, urinary tract infections are determined not by the mere presence of bacteria in a urine sample, but by the magnitude of bacteria (>105 CFU/ml) in the sample. 1, 2, 3
Contributors and Attributions
Kelly C. Burke (College of the Canyons)