Measure background particulates

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. Step-by-step instructions are given below for how to measure the concentration objects in the growth medium.

Step by step

1. Use a serological pipette to collect a small sample of the cultivation medium.
2. Vortex 30 seconds at max speed to ensure an even distribution of particles
3. Dilute 1:100 in diluent

   1. Add 101 µL of sample to 10 mL of diluent.
   2. Vortex 10 sec., max speed.
4. Transfer the tubing kit to the diluted sample.
5. Click Measure .

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.

Results and implications

We focus on the cells/mL concentration as it may artificially increase the perceived cell count. The total/mL value is also important, but mainly because higher dilution might be necessary if there's notable particulate contribution from a specific source.

Summary

You have now done a BactoBox measurement on the growth medium prior to inoculation with bacteria.

In the next page Mitigate high background we will first discuss if the background is negligible or important. In the latter case, we provide three mitigation strategies to minimize the impact of background particulates.