Estimating microbial population data from optical density

Abstract

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.

Apparent diameter and cell density of yeast strains with different ploidy

“…It depends on the radius of the scatterer, wavelength of incident light and refractive indices of the scatterer and the media, respectively 1 . Whereas the proportionality constants k significantly depended on the bacterial cell size 22 , there was relatively less difference in the constants k between yeast strains in the current study.…”

Isolation and Characterization of aHalomonasSpecies for Non-Axenic Growth-Associated Production of Bio-Polyesters from Sustainable Feedstocks

“…Cells from the exponential phase of shake-flask culture on NB-saline medium (1 M of sodium chloride) were harvested by centrifugation (4480×g for 20 minutes) and resuspended in deionized water, while the OD was measured before the osmotic shock, as well as at 1 min, 10 min, 20 min, and 40 min thereafter. Further, colony-forming units (CFU) of the original culture, as well as the cell-suspension after the osmotic shock were determined by plating 100 µ L of in 10 4 -fold dilutions, based on the initial OD600 (0.6) of the culture at the point of collection, which had an estimated cell-count of ∼ 4.7×10 7 cells/mL [83].…”

Verification of a method using magnetic bead enrichment and nucleic acid extraction to improve the molecular detection of bacterial contamination in blood components

“…Then 50 µL cultured samples was inoculated into 5 mL of LB broth and cultured for 3 h under the same conditions. When the optical density at 600 nm (OD 600 ) reached 1, the concentration of B. cereus was determined to be 10 7 CFU/mL, and the concentration of the other three bacterial strains was found to be 10 8 CFU/mL ( 42 – 45 ). Bacterial pellets were harvested by centrifuging 1 mL cultured sample at 8,000 rpm and room temperature for 10 min.…”