DEVICES FOR MEASURING TURBIDITY ARE PUT "UNDER THE MICROSCOPE"
Here we take an in-depth look at how spectrophotometers compare to MicrobeMeter and the key advantages of MicrobeMeter.
We tested the linearity of measurement response of 3 different spectrophotometers and a MicrobeMeter.
We used three different cell cultures which were expected to have different light scattering properties: Escherichia coli, Shewanella oneidensis and Schizosaccharomyces pombe.
For each organism, 2-fold serial dilutions were prepared harvesting cells via centrifugation and re-suspending in standard phosphate-buffered saline (PBS).
Each cell dilution series was measured using MicrobeMeter with three tubes (P1, P2, P3) containing the same culture samples, one tube containing PBS only (i.e., “blank” control) and used for temperature correction.
LINEAR TURBIDITY MEASUREMENTS
The same cell culture serial dilutions were measured using 3 different spectrophotometers and the 3 ports of the same MicrobeMeter (P1, P2 and P3) with a blank control test tube.
All the tested cell culture dilutions turbidity measurements were linear (Figure A below) across all devices tested. As expected, all devices had different actual values from each other (Figure A below), confirming that turbidity measurements cannot be compared between devices . The average of the slopes of the 3 serial dilutions was compared against the calculated slope of the serial dilution, which is expected to be ln(2) given 2-fold dilutions performed.
See the graphical results below.
Figure A = Regression analysis of the turbidity measurements
Figure B = Slopes of the turbidity measurements. (dots = slope, bars = average, standard deviation = error bars)
Figures A and B – MicrobeMeter samples in Port 1, Port 2 and Port 3 compared with 3 different spectrophotometers.
MICROBEMETER HAS KEY ADVANTAGES OVER SPECTROPHOTOMETERS
From the figures above we can deduce the following:
1. MicrobeMeter has lower variability compared to spectrophotometers (Figure B).
The averages of the slopes produced by 3 ports of MicrobeMeter (P1, P2, P3) displayed lower variability compared to slopes from spectrophotometers.
2. MicrobeMeter is as accurate and with less variability as spectrophotometers (Figure B).
The results show turbidity measurements’ using MicrobeMeter allow cell density estimation as accurately as spectrophotometers with MicrobeMeter having less variability across estimates.
3. MicrobeMeter is less sensitive than spectrophotometers to differences in light scattering caused by different cell types (Figure B).
MicrobeMeter is probably less sensitive to differences in scattering by different cell types compared to the spectrophotometers tested.
MicrobeMeter has lower variability compared to spectrophotometers and is as accurate and with less variability. Also, MicrobeMeter is less sensitive than spectrophotometers to differences in light scattering caused by different cell types.
Estimating cell culture density by turbidity with MicrobeMeter is comparable to, or better than spectrophotometers.
 Matlock BC, et al. (2011) Analyzing Differences in Bacterial Optical Density Measurements between Spectrophotometers. Thermo Scientific, Technical Note: 52236 (Madison, WI).