Table 4.
Characteristic features of some methods for determination of cell viability in bacterial inoculants
| Plate‐countinga | Plate reader – absorbance (OD600)a | Plate reader – luminescence (BacTiter‐Glo™) b | Plate reader – fluorescence (LIVE/DEAD BacLight™) b | Microscopy – fluorescence (LIVE/DEAD BacLight™)b | Flow cytometry – fluorescence (LIVE/DEAD BacLight™)b | PMA‐qPCRa | Microcalorimetrya | Intracellular phototautomerismc | |
|---|---|---|---|---|---|---|---|---|---|
| Approximate detection limit | 1 CFU (resolution depending on incubated volume) | 107 cells per ml (lower when measuring growth time to detection) | 101 to 103 cells per well (100 μl), depending on bacterial species | 105 to 106 cells per ml, depending on bacterial species | 2 × 105 to 2 × 106 cells per ml (depending on bacterial species) | 104 cells per ml | 102 cells (depending on dead cell background) | 3 × 104 cells per ml | 106 cells per ml |
| Duration of assay | Days | Minutes | Minutes | Minutes | Minutes to hours | Minutes to hours | Hours | 1 Hour | Minutes to hours |
| Opaque samples | Possible | Limited (depending on ratio of sample to rehydration media) | No | No | No | No | Limited | Possible | No |
| Specificity | Limited (selective medium, morphology) | No | No | No | No | No | High | No | No |
| Automation possible | Limited | Yes | Yes | Yes | No | Yes | Yes | Yes | Yes |
| Decisive parameter for detection | Culturability | Cell biomass | Metabolic activity (ATP) | Membrane integrity | Membrane integrity | Membrane integrity | Membrane integrity | Metabolic activity (heat) | Cytosolic pH homeostasis |
b. According to the manufacturer's instructions (LIVE/DEAD® BacLight™ Bacterial Viability Kit, Thermo Fisher Scientific Waltham, MA, USA; BacTiter‐Glo™ Microbial Cell Viability Assay, Promega, Fitchburg, WI, USA).
c. According to Kort et al., 2010.