Enumerating the viable and total cell concentration of a population of a microbial isolate can be a really laborious task for a microbiologist

Question

Especially when a microbiologist studies the same isolate for several years, it often becomes practical to determine the relationship between optical density (OD) and cell concentration. Once this relationship (determined by a standard curve) is determined, the OD of an isolate in a broth can be routinely used to determine the population's concentration. Why must a standard curve be prepared for each isolate when using OD measurements to determine cell concentration? Also describe an experiment that would generate this type of standard curve.
What will be an ideal response?

Answer 1

Answer: Answers will vary, but it should be noted that a particular OD value will correspond to a specific cell concentration. Cell because different shapes and sizes of microorganisms. One such example could be a culture of Citricella sp. SE45 was determined to have an OD540 of 0.485. This OD fit into the already-constructed standard curve to indicate that 5 × 105 viable cells are in each milliliter of broth, which can be helpful in experiments where the final cell concentration or number is critical. To initially create the standard curve, a traditional growth curve experiment could be performed over time where both OD and cell concentration (viable with viability plating or total with direct counts) would be measured. The values of OD and cell concentration for each time point would then be used to create a standard curve, and a linear regression curve would show the relationship of OD to cell concentration such that subsequent experiments OD could be measured as a proxy for cell concentration.