Question

Given the need for specific bacterial concentrations without available growth curves, which method might prove reliable for estimating cell counts when OD (Optical Density) measurements are present but not CFU (Colony Forming Units) data?

A) Use of silicon microspheres to estimate bacterial sizes, allowing OD-to-CFU conversions.
B) Employing a standardized dilution series to correlate OD readings with CFU counts for each bacterial culture.
C) Measuring bacterial cell sizes using a microscope and comparing them with known standards for OD-to-CFU conversions.
D) Directly converting OD measurements to CFU counts based on an assumed linear relationship.

Answer 1

The most accurate method for estimating bacterial cell counts without CFU data is to use a standardized dilution series to correlate OD readings with CFU counts, creating a calibration curve for future estimations.

Step-by-step explanation:

To estimate bacterial cell counts without direct CFU data, the most reliable option provided is B) employing a standardized dilution series to correlate OD readings with CFU counts for each bacterial culture. This approach involves creating a calibration curve by performing a viable plate count of samples taken from cultures having a range of absorbance or OD values. The turbidity, as measured by a spectrophotometer, is plotted as a function of cell density to establish the relationship between OD readings and CFU counts. Once established, this curve can be utilized to estimate the cell counts of samples under similar conditions.

Option A involves a complex assessment of bacterial sizes which may not provide a reliable conversion of OD to CFU across different types of bacteria. Option C is also unfeasible because it requires microscopic measurements which are not always practical or consistent. Option D assumes a linear relationship which is rarely accurate due to various factors affecting the correlation between OD and CFU counts in different growth phases or conditions.