Cell Concentration Linear Range and Reliability
Serial two-fold dilutions of rehydrated yeast were counted on the Cellometer Auto X4 (10x) to determine the linear range for reliable yeast concentration measurements. The range of concentration that can be measured on the instrument is dependent on the size of the cell being counted (i.e. the range decreases as cell size increases). The Muntons strain is approximately 4.5 µm in diameter when rehydrated, and was selected for this experiment due to its intermediate size when compared to other yeast strains such as those used for lager beer or wine production. The upper limit for accurate yeast counting, as determined by examining counted images, represented a four-fold dilution of the original concentrated yeast suspension (Dilution 2) at 6.6 x 107 cells/mL. Serial dilutions of this sample were counted until the lower limit was reached (Dilution 6) at a concentration of 4.17 x 106cells/mL.
Plotting of the measured concentration versus the concentration factor (inverse of the dilution factor) resulted in a linear relationship with an R2 of 0.9968. Thus the linear range for counting Muntons yeast (and other similarly sized strains around 4.5 µm in diameter) on the Cellometer Auto X4 (10x) is between 4 x 106 and 6.6 x 107 cells/mL (Figure 1A).
Repeated measurements were performed on the sample to determine the reliability of counting by calculating the Coefficient of Variation (CV). Within the linear range for counting yeast on the Cellometer Auto X4 (10x), the CV was between 4% and 13% (Figure 1B).