Hit the right concentration

Samples with high concentration are usually turbid.

Samples with low concentration are usually transparent.

Users that produce bacteria usually have high concentrations.

If the concentration in your sample is too high, we dilute it. If the concentration is too low, we concentrate your sample. In either case, we try to hit the target of 0.5–4 million cells/mL. See the table below for our recommendations:

Concentration in your sample	Dilution	How-to guide(s)
5 · 1011 cells/mL	10-6	Three Dilute 1:100 in sequence.
5 · 1010 cells/mL	10-5	Dilute 1:100 000.
5 · 109 cells/mL	10-4	Two Dilute 1:100 in sequence.
5 · 108 cells/mL	1 0-3	First Dilute 1:10 then Dilute 1:100.
5 · 107 cells/mL	10-2	Dilute 1:100. ⚠️ You may have to use custom diluent.
5 · 106 cells/mL	1:10	Dilute 1:10. ⚠️ You may have to use custom diluent.
5 · 105 cells/mL	N/A	⚠️ You may have to use custom diluent.
≤5 · 104 cells/mL	N/A	See Concentrate your sample.

You can do combinations to get even high dilution factors. Just like how we do three Dilute 1:100 steps in a row to get a 1:1 000 000 dilution overall.

Target 0.5–4 million cells/mL for fast results

The more things to count, the faster we are certain about the concentration. Give BactoBox® something to work with and it triggers the Fast results feature ⏩.

Make a dilution series and measure the most diluted sample first. Aim for 0.5–4 million cells/mL.

Don't know the concentration of your sample?

Make a dilution series and measure the most diluted sample first. This avoids clogging your BactoBox® setup. It also avoids carry-over from your previous sample vial.

Once you are above the lower limit of detection (30 000 cells/mL), target a concentration of 0.5–4 million cells/mL.

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.

Example

E. coli reaches concentrations up to 10¹¹ cells/mL during fed-batch culture. See Shake flask or fermenter for a dedicated protocol.

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

• 30 000–5 000 000 total/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.