BacTotal-10

Our recommended default measurement program. What it counts, and how that compares to CFU.

What BacTotal-10 counts

BacTotal-10 counts whole bacterial cells in your sample. The result is cells/mL.

In general, these all count:

• A cell that is dividing

• A cell that has stopped dividing

• A cell that no longer forms a colony

• A cell that takes up propidium iodide

A cell that has lysed is not counted. A cell that has come apart is no longer there.

There are exceptions. Heat or alcohol can change a cell's electrical properties so much that BacTotal-10 no longer sees it as a cell. The same can happen to aged cells of some Gram-positive species. See Inactivated bacteria.

Particles that do not look like bacteria, such as debris, count towards total/mL but not cells/mL.

Cells/mL is not OD600. OD is often read as a rough cell count, but it is not one. It adds up cell number, cell size and shape, the optical properties of the cells, and the medium. When OD behaves unexpectedly, one of these has usually changed. See Understanding OD600.

How cells/mL compares to CFU

CFU counts the cells that form a colony under your plating conditions. That is culturability.

We calibrated cells/mL against CFU/mL for six species in a peer-reviewed study (Jordal et al., 2025). BacTotal-10 multiplies the raw cell count by 1.46, the empirical concentration correction (ECC) factor, so that cells/mL ≈ CFU/mL for actively growing cultures. See Precision and accuracy.

Your own plate counts may differ from cells/mL by a small factor, because organisms and plating methods differ. For a given process, that factor stays the same while the culture grows. You can use it to convert cells/mL to your CFU/mL.

Cells/mL and CFU/mL track each other closely through exponential and early stationary phase. They separate in decline phase. Cells stop forming colonies, so CFU falls. BacTotal-10 does not see that loss.

K. aerogenes in TSB. BactoBox® cells/mL (lavender) and CFU/mL (yellow), triplicates. The two agree while the culture grows. In decline phase (red box), CFU falls to about 10 % of its peak by 24 hours, while cells/mL stays close to flat.

Harvest as soon as BactoBox® shows that growth has stopped, or when cell size has plateaued. Use whichever signal works better for your process. See Identifying the harvest point.

BacTotal-10 does not measure live-dead

BacTotal-10 does not tell live cells from dead cells. We do not see a need for it in growth work. Only live cells divide, so a rising cells/mL means the culture is growing, and any cell death is negligible. When conditions get worse, cells stop dividing first and die later.

Read more in Are live-dead measurements needed?

Why BacTotal-10 is the default

We recommend BacTotal-10 for all work. BactoBox® uses it by default when you press Measure. It works across species and media with no setup. Its limits are known, and each one has a workaround.

Limit	What to do
A clump or chain counts as one cell	Break up cell clumps
Some media add background at low dilutions	Check medium background
Loss of culturability is not seen	Harvest when growth stops
Some heat-treated, alcohol-treated or aged cells are not counted	Talk to SBT about Custom gating
Species are not told apart	The count is the sum of everything growing

BacTotal-10 is short for BacTotal_v2024-10.

Changing the measurement program

Talk to SBT before you use anything other than BacTotal-10. We agree any change with you first, so you know what the new numbers mean. See Custom gating and Legacy gating settings. Contact us.