Correlation with plate counts

BactoBox® shows strong agreement with plate count measurements for most Active cultures. I.e., when the culture is in exponential, deceleration, and stationary Growth phases.

Correlation across a growth curve

The below figure compares plate counts (CFU/mL, yellow) with BactoBox® (lavender). Plate counts and BactoBox® curves are practically superimposed, and R² ≈ 1 for the linear regression on the log-log transformed data. This means that the methods are strongly correlated across exponential, deceleration, and early-stationary stage.

K. aerogenes growth curve investigated with BactoBox® (lavender) and plate counts (yellow). Triplicate repeats were done for each data point. Additional head-to-head growth curves for E. coli, A. baumannii, P. fluorescens, S. epidermidis, and L. innocua are available in Journal of Microbiological Methods.

Comparison of absolute numbers

The peer-reviewed publication in Journal of Microbiological Methods demonstrates full head-to-head growth curves for 6 bacteria. The chosen species are different in terms of size, morphology and envelope constitution. All growth curves showed strong correlation (R² ≈ 1.00) for active cultures.

Correlation does not necessarily imply that the absolute numbers are the same. The table below shows the BactoBox®-to-CFU comparisons for the 6 bacteria. Most direct comparisons were within ±0.1 log units (i.e. within ~25% difference). The geomean cell-to-CFU ratio is also provided in the table. Geomean is generally close to 1, i.e. when a cell is detected on BactoBox® it practically corresponds to one colony on a plate.

	S. epidermidis	E. coli	K. aerogenes	A. baumannii	L. innocua	P. fluorescens
Strain	ATCC 12228	ATCC 8739	ATCC 13048	ATCC 12457	ATCC 33090	ATCC 13525
Approx. size	0.8 × 1.0 µm	1.0 × 3.0 µm	0.5 × 1.5 µm	0.6 × 1.0 µm	0.7 × 2.0 µm	0.5 × 1.2 µm
Gram status	Gram+	Gram-	Gram-	Gram+	Gram+	Gram-
Within ±0.1 log	7 out of 7	5 out of 6	8 out of 8	3 out of 7	7 out of 7	7 out of 7
Cells-to-CFU	1.09	1.12	0.99	1.35	0.89	0.90

Correlation for dilutions of the same sample

The above plot demonstrates the correlation across a growth curve. Correlation between BactoBox® and CFU is also strong across different dilutions of the same sample as demonstrated on the plot below where the same sample was diluted and measured head-to-head with BactoBox® and plate counts.

The slope of the regression line is 0.9947. This is practically a perfect slope of one meaning that for every S. epidermidis detected on BactoBox® you will also get one colony by plate counts. The R² ≈ 1 signifies the strong linear relationship between the two methods. In most cases, BactoBox® demonstrates greater precision than the CFU method. For example the most concentrated sample has a coefficient of variation (CV) of 3 % for BactoBox®, while the CV is 35 % for the plate count method.

Head-to-head comparison of BactoBox® and plate count method for dilutions of the same Staphylococcus epidermidis sample. X-axis represents plate count arithmetic mean and y-axis represents BactoBox® arithmetic mean. All measurements were performed in technical triplicates. The table displays the arithmetic mean and the coefficient of variation (CV) for each data point. CV ≤ 5 % are highlighted in green.