Journal Article

Estimating microbial population data from optical density

Mira, Portia, Hall, Barry G., Yeh, Pamela

2022

Overview

The spectrophotometer has been used for decades to measure the density of bacterial populations as the turbidity expressed as optical density–OD. However, the OD alone is an unreliable metric and is only proportionately accurate to cell titers to about an OD of 0.1. The relationship between OD and cell titer depends on the configuration of the spectrophotometer, the length of the light path through the culture, the size of the bacterial cells, and the cell culture density. We demonstrate the importance of plate reader calibration to identify the exact relationship between OD and cells/mL. We use four bacterial genera and two sizes of micro-titer plates (96-well and 384-well) to show that the cell/ml per unit OD depends heavily on the bacterial cell size and plate size. We applied our calibration curve to real growth curve data and conclude the cells/mL–rather than OD–is a metric that can be used to directly compare results across experiments, labs, instruments, and species.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Analysis / Bacteria / Biology and Life Sciences / Calibration / Cell culture / Cell size / E coli / Engineering and Technology / Enzymes / Evaluation / Lab Protocol / Light / Medicine and Health Sciences / Microbial populations / Microorganisms / Optical density / Optical detectors / Physical Sciences / Population density / Research and Analysis Methods / Sensors / Spectrophotometers / Spectrophotometry - methods / Turbidity