Concentrate your sample

It is generally not recommended to use BactoBox® for measuring samples with very low bacterial concentrations. This page is a collection of tips and tricks for how to do so.

Too low bacterial concentration

Samples with low concentration are usually transparent.

Your sample must have at least 30 000 cells/mL to measure it with BactoBox®.

Want to verify the absence of bacteria?

This is not the ideal use case for BactoBox®. The lower limit of detection is 30 000 cells/mL.

My sample stock contains around 100 000 cells/mL

This is just above the lower limit of detection but not by a lot.

Theoretically, your sample is good to go since the cells/mL concentration is well above the threshold. In practice, however, you must both:

• Hit the right electrical conductivity

• Reach the minimum sample volume of 4 mL

Already achieved both? Well, then you're done! Otherwise, this is where it gets a bit tricky. See:

Hit the right conductivity

Specifically the section about low dilution factors.

My sample stock is below the limit of detection

You must concentrate your sample before you measure on it with BactoBox®. We recommend that you use a centrifuge together with membrane filter. We describe this filter-centrifugation approach here:

Filter-centrifuge your sample

Motivation

BactoBox® counts individual particles. If there are too few particles, the concentration estimate is too uncertain. If there are too many particles, we can't tell them apart. Therefore, we have limits of detection (LoD). BactoBox® outputs concentrations in these ranges:

• 30 000–5 000 000 cells/mL (3e4 to 5e6 cells/mL)

• 30 000–5 000 000 total/mL (3e4 to 5e6 cells/mL)

See limits of detection for more details.

BactoBox® uses an electric field to measure individual cells. Below the LoD (top), next-to-nothing enters the electric field and the cells/mL concentration is uncertain. Within the LoD (middle), individual cells enter the electric field so we can tell them apart and count them. Above the LoD (bottom), multiple cells enter the electric field at the same time and we can't tell them apart.