> For the complete documentation index, see [llms.txt](https://help.sbtinstruments.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.sbtinstruments.com/tutorials/measure-vitroid-tm-disc/summary.md).

# Summary

In this tutorial you learned how to dissolve a Vitroids™ disc and prepare the bacterial suspension for BactoBox® analyses.

## Calculate cell concentration of non-diluted suspension

You just did your first BactoBox® measurement. The result on the BactoBox® is for the diluted sample. Always remember to multiply the obtained result with the dilution factor to get the concentration of the non-diluted suspension.

<table><thead><tr><th width="171.6666259765625">BactoBox® dilution</th><th width="213">BactoBox® concentration</th><th>Non-diluted suspension</th></tr></thead><tbody><tr><td><mark style="color:$info;">100</mark></td><td><mark style="color:$info;">89 000 cells/mL</mark></td><td><mark style="color:$info;">100 × 89 000 cells/mL = 8 900 000 cells/mL</mark></td></tr></tbody></table>

## Comparison between CFU and BactoBox® results

We can estimate the number of cells in the Vitroids™ disc from the measured cell concentration after dissolution. We assume that the total volume remains 110 µL (0.110 ml) after the disc is added. That gives a volume of 0.110 ml/disc.

1. Measure the cell concentration in the dissolved sample:\
   **8,900,000 cells/mL**
2. Multiply by the dissolution volume:\
   **8,900,000 cells/mL × 0.110 mL/disc = 979,000 cells/disc**

To develop this tutorial, we repeated the procedure with **three Vitroids™ discs from the same lot**. The table below summarizes the results (all values are reported as **cells/disc**).

<table><thead><tr><th width="118.333251953125">#1</th><th width="102">#2</th><th width="134.3333740234375">#3</th><th>Arithmetic mean ± Standard deviation</th></tr></thead><tbody><tr><td>979 000</td><td>970 000</td><td>1 100 000</td><td>1 000 000 ± 90 000 cells/disc</td></tr></tbody></table>

The concentration is stated by Sigma/Merck as 50,000-150,000 CFU mean value range. This is \~1 log below the results obtained with the BactoBox® measurements. It is normal to see cells ≠ CFU for formulated, stored products, see the box for more information.

{% hint style="info" %}

## BactoBox detects all forms of bacteria. Plate counts only detects culturable cells.

A plate count only measures the culturable cells and does not detect VBNC forms of bacteria. BactoBox® detects viable, dead and VBNC forms of bacteria. BactoBox® shows [great correlation](/mpd/cell-growth/correlation-with-plate-counts.md) for most [Active cultures](/mpd/cell-growth/active-cultures.md) while BactoBox® measurements on bacteria in dormant and stressed states may show [Divergence from plate counts](/mpd/cell-growth/divergence-from-plate-counts.md).
{% endhint %}

## BactoBox® skills

After successfully completing this tutorial you have acquired the following skills:

<i class="fa-bacteria">:bacteria:</i> Disaggregrate bacterial clumps by vortexing

<i class="fa-boxing-glove">:boxing-glove:</i> Make a 1:100 dilution of a dilute bacterial sample and measure on BactoBox®

<i class="fa-calculator-simple">:calculator-simple:</i> Calculate cell concentrations of the non-diluted bacterial suspension

## Next steps

This, first tutorial was a quick and simple introduction to a bacterial measurements.

We have another great tutorial lined up for you: [Measure a dense culture](/tutorials/measure-overnight-culture.md). You will prepare a dense culture using a Vitroids™ disc (or an in-house *E. coli* cryo stock). After overnight incubation you will learn how to dilute the sample 1:10,000 to hit the right concentration.


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