Inactivation by alcohol

Alcohols like 70% ethanol or 70% isopropanol destabilize bacterial lipid membranes into a disordered state that no longer impedes electricity. The conductive cell wall survives the alcohol treatment.

Does BacTotal-10 count alcohol-inactivated bacteria as cells?

Mostly not. Once treated with e.g. 70% ethanol or 70% isopropanol, most vegetative bacteria move outside the BacTotal-10 cell-definition.

The alcohol-inactivated populations may be included by custom gating. This is an advanced feature. We only support advanced features through a custom solution. Contact support for details.

Alcohol-inactivated bacteria and BacTotal-10

The default BactoBox® configuration uses BacTotal-10. Objects classified as cells are found within the region with lavender shading. The distributions correspond to cultures before (green) and after (red) treatment with 70% isopropanol for 5 min.

The plots below are from Escherichia coli, Flavobacterium psychrophilum, Klebsiella aerogenes, and Salmonella enteritidis. Alcohol-treatment converts these Gram-negative bacteria to highly conductive objects found outside the BacTotal-10 cell-definition.

Alcohol-inactivated Salmonella objects are found in-between the cells and particulates range. Therefore, a proportion of the alcohol-treated Salmonella will still be counted, but the cell concentration may be underestimated unless custom gating is used.

Inactivation of Gram-negative bacteria with 70% isopropanol. The untreated cultures (green) are found within the BacTotal-10 cell-definition, while the alcohol-treated cultures (red) are excluded from BacTotal-10.

The electrical changes are similar for Gram-positive bacteria. The plots below are from alcohol-treated cultures of Bacillus subtilis, Clostridium difficile, Listeria innocua, and Staphylococcus epidermidis. The alcohol-treated cells are converted to highly conductive objects found outside the BacTotal-10 cell-definition.

Inactivation of Gram-positive bacteria with 70% isopropanol. The untreated cultures (green) are found within the BacTotal-10 cell-definition, while the alcohol-treated cultures (red) are excluded from BacTotal-10.

Summary

When cells are treated with alcohols like 70% ethanol and 70% isopropanol they move outside the BacTotal-10 cell-definition. Custom gating is required for BactoBox® to enumerate alcohol-treated cells.

Advanced feature 🧩

Custom gating is an advanced feature. We only support advanced features through a custom solution. Contact support for details.