Final answer:
The turbidity of a culture is measured using a spectrophotometer as an indirect method to estimate bacterial cell populations, with the calibration curve enabling accurate cell density estimations.
Step-by-step explanation:
Indirect Measurement of Bacterial Cell Populations
The turbidity of a culture is used as an indirect method to estimate bacterial cell populations. This method involves using a spectrophotometer to measure the cloudiness of a liquid suspension. A light beam is transmitted through the suspension and the optical density (absorbance) or percent transmission is measured. Higher turbidity correlates with an increased bacterial count, as more cells will scatter and absorb light, reducing the amount that reaches the detector.
To accurately estimate the number of bacterial cells, a calibration curve is necessary. This curve is established by initially conducting viable plate counts on samples with known turbidity levels, thus correlating turbidity readings with actual cell counts. The calibration curve can then be referred to in future tests to estimate the cell density of similar cultures.