Quick answer
CFU stands for colony forming units, a count of live microbes that can grow in a lab test. AFU stands for active fluorescent units, a count made by flow cytometry, used for bacteria like Akkermansia. A higher number isn't automatically better; the strain, the count per serve and how the product is stored all matter.
CFU
Colony forming units
AFU
Active fluorescent units
Typical labels
1 to 50+ billion per serve
Look for
Strain names and count per serve
What does CFU mean?
CFU counts how many microbes in a sample are able to grow and form a colony on a lab plate. A label might say "12 billion CFU per capsule", meaning that many viable microbes per capsule.
What does AFU mean?
AFU counts bacterial cells using flow cytometry, a method that uses fluorescent dyes and lasers. It's used for species that are hard to grow on lab plates, such as Akkermansia muciniphila.
MAYN probiotics compared
| Product | Microbe | Count per serve | Extra |
|---|---|---|---|
| Akkermansia | Akkermansia muciniphila | 1 billion AFU | Prebiotic inulin |
| Lactobacillus Gasseri | L. gasseri | 12 billion CFU | Prebiotic inulin |
| Lactobacillus Reuteri Complex | L. reuteri complex | 22 billion CFU | Prebiotic inulin |
| Saccharomyces Boulardii | S. boulardii (a yeast) | 10 billion CFU | – |
How to compare probiotics
- Check the strain, not just the species. Strains have extra letters or numbers after the name.
- Check the count per serve and whether it's guaranteed at manufacture or until the expiry date.
- Check storage directions: some probiotics need refrigeration, others are shelf-stable.
- Pick one that suits your routine and take it as the label directs.
Tip: A higher CFU number isn't automatically better. Different species and strains are used in very different amounts.
Frequently asked questions
Is a higher CFU count better?
Not necessarily. The strain and the amount used for that strain matter more than the biggest number.
Do probiotics need to be refrigerated?
Some do and some don't. Follow the storage directions on the label.
What's the difference between CFU and AFU?
CFU counts microbes that grow on a lab plate; AFU counts cells using flow cytometry. They're different methods, so the numbers can't be compared directly.
Keep reading
This article is general information only and is not medical advice. Always read the label and follow the directions for use. Dietary supplements should not replace a balanced diet. If you are pregnant, breastfeeding, taking medication or have a medical condition, speak with your doctor or pharmacist before taking a new supplement.
