# Check growth medium

Certain growth media have unexpectedly high particle concentrations. This can lead to confusing results, particularly during the lag phase when bacterial concentration is still low.

Here, you will measure a 1:100 dilution of the growth medium **prior** to inoculation. If the cells/mL concentration is below 30,000 cells/mL the growth medium contribution is negligible and you can skip ahead to the next section. If the cells/mL exceeds 30,000 cells/mL a suitable workaround must be chosen. See the info box at the bottom of this page for more information.

{% stepper %}
{% step %}
**Prepare the sample for BactoBox® measurement**

1. Use a serological pipette to collect a small sample from the shake flask.
2. Return the shake flask to the incubator shaker.
3. Vortex 30 seconds at max speed to ensure an even distribution of particles
4. Dilute 1:100 in diluent by adding 101 µL of sample to 10 mL of diluent. Vortex 10 sec., max speed.
5. Transfer the tubing kit to the diluted sample.

<figure><img src="/files/tUo0C4h2nhT5bte8twIs" alt=""><figcaption></figcaption></figure>
{% endstep %}

{% step %}
**Measure the diluted sample on BactoBox®**

7. Click the <kbd><mark style="background-color:purple;">Measure<mark style="background-color:purple;"></kbd> button in Access.
8. Add metadata:
   1. Dilution: <kbd>100</kbd>.
   2. Label: <kbd>medium\_ctrl</kbd>.

<figure><img src="/files/8QhtdryJlWbwjWfcOkE3" alt=""><figcaption></figcaption></figure>

{% hint style="danger" %}

## Do you get the error *conductivity too high*?

Some cultivation media have very high conductivity and a 1:100 dilution in standard diluent is not sufficient to bring the diluted sample within the accepted conductivity limits.

You can typically solve this issue by using a 1:201 dilution: Simply add 50 µL of sample to 10 mL of diluent. For more information, please see the section [Hit the right conductivity](/protocols/prepare-your-sample/hit-the-right-conductivity.md).
{% endhint %}
{% endstep %}

{% step %}
**Clean the device**

9. Transfer the tubing kit to the disinfection vial.
10. Click <kbd>Clean</kbd>.
    {% endstep %}
    {% endstepper %}

## Summary

Now you know the particle contribution from the growth medium. Next, measure the bacterial concentration in your starter culture.

## Mitigate background particulates in growth medium

{% hint style="info" %}

## Does the cells/mL exceed 30,000 cells/mL at 1:100 dilution?

Several strategies are possible if the [particle concentration in the medium is substantial](https://github.com/sbtinstruments/docsites/blob/main/help/protocols/prepare-your-sample/focus-on-target-objects/mitigate-high-background.md). Consult [Mitigate high background](/protocols/prepare-your-sample/focus-on-target-objects/mitigate-high-background.md) for more information.
{% endhint %}


---

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