AFUs (Active Florescent Units) and CFUs (Colony Forming Units) are both units of measuring the number of microbes present in bacterial colonies. While CFUs are the industry standard, AFUs are an emerging measure based on more advanced technology that can distinguish active microbes, as opposed to just those that are reproducing. In order to most accurately measure the potency of our products, Pendulum uses AFUs to measure the amount of each probiotic strain included in a serving of a supplement.
Benefits of using AFUs
Measuring microbes that are doing the work
Many of the mechanisms of action of probiotics require that the probiotic be active but not actively multiplying. A designation used to identify these microbes is VBNC (Viable But Nonculturable). These particular active microbes, not counted by CFUs, are devoting their energy to the key actions that make a probiotic effective instead of spending that energy on reproduction. Actions such as:
- Production of specific metabolites that are continuously secreted outside the bacterial cell (SCFA, vitamins)
- Maintaining cell wall compounds
- Production of specific proteins outside the cells
Doesn't rely on conditions of plating
To count CFUs, probiotic strains are introduced to a culture medium in which they will begin to reproduce. Once certain conditions are met and bacterial colonies become visible to the naked eye, they are counted and the number of total microbes is estimated based on this count. This process is called "plating" or "plate counting."
Plate counting is limited by its dependence on a combination of culture conditions such as nutrients in the culture medium and temperature.
More accurate measurement using advanced technology
Measuring AFUs requires the application of flow cytometry. Each cell is marked with fluorescent marker if it is both alive and active. Then these alive and active cells are counted as they pass through a narrow tube. A laser pointed at the tube registers each cell with the fluorescent marker that passes it.
This type of count focuses on all the viable cells, and is much more accurate than a plate count.