Probiotic strains explained: species, CFU, and prebiotics
By Plum Supplements · 8 min read
Probiotics are live microorganisms, usually bacteria, that support digestive health when taken in adequate amounts. A strain is a specific type within a species, identified by a code after the name. CFU, or colony forming units, counts how many live organisms a product contains. Prebiotics are fibers that feed beneficial gut bacteria.
What is the difference between a genus, species, and strain?
Probiotic names follow the same naming system as the rest of biology. Take Lactobacillus acidophilus. "Lactobacillus" is the genus, a broad family. "acidophilus" is the species. A strain is a specific, identified version of that species, usually written as a code after the name, such as "NCFM" or "DDS-1."
| Level | Example | What it tells you |
|---|---|---|
| Genus | Lactobacillus | A broad group of related bacteria |
| Species | Lactobacillus acidophilus | A specific kind within the group |
| Strain | L. acidophilus followed by a strain code | One identified, traceable culture |
Why it matters: research on probiotics is often strain specific. A study on one strain does not necessarily apply to another strain of the same species. Labels that list strain codes let you look up that exact culture. Many products, including ours, list species without strain codes, which is common but gives you less to look up.
What does CFU mean?
CFU stands for colony forming units, an estimate of how many viable microorganisms are present. A label reading "40 billion CFU" is claiming roughly 40 billion live organisms per serving. Two details matter: when that count was measured, and whether a bigger number is actually useful.
At time of manufacture vs through expiration
Probiotics are alive, and their numbers decline over time. Some labels state CFU "at time of manufacture," others "through expiration." A count through expiration is a stronger promise, since it accounts for that decline. Neither is wrong, but you should know which one you are reading.
Is more CFU better?
Not automatically. Studies have used a wide range of amounts, from around one billion to well over 50 billion CFU. The species and strains, how well they survive, and consistent daily use matter at least as much as the headline number.
What do prebiotics do?
Prebiotics are types of fiber that you cannot digest but your gut bacteria can. They act as food for beneficial microbes already living in your digestive tract. Common prebiotics include inulin, fructooligosaccharides (FOS), and certain resistant starches, which also occur naturally in foods like onions, garlic, leeks, asparagus, bananas, and oats.
A product that combines probiotics and prebiotics is sometimes called a synbiotic. The idea is simple: deliver the bacteria and some food for them in the same serving. Prebiotics do not replace a fiber-rich diet, they supplement it.
How do probiotics survive storage and digestion?
Two challenges stand between a probiotic capsule and your intestines: the shelf and your stomach. On the shelf, heat, humidity, and time reduce live counts. In the body, stomach acid can reduce them further. Manufacturers use several approaches to address both.
- Shelf-stable formulas use dried cultures and protective packaging so they do not require refrigeration.
- Delayed release capsules are designed to resist stomach acid and open later in digestion.
- Storing the bottle somewhere cool and dry, with the lid tight, helps preserve counts.
- Avoid leaving probiotics in a hot car or a steamy bathroom.
What to check on a probiotic label
- Genus and species, and strain codes if listed.
- Total CFU, and whether it is measured at manufacture or through expiration.
- Total blend weight, and whether individual amounts are listed.
- Any prebiotic fiber and its amount.
- Storage instructions and capsule type, such as delayed release.
- Third-party testing documentation.
How Plum Probiotic 40 Billion is labeled
Our Probiotic 40 Billion with Prebiotics is a shelf-stable blend providing 40 billion CFU at time of manufacture in a delayed release vegetable capsule. The label lists four species, Lactobacillus acidophilus, Lactobacillus plantarum, Bifidobacterium lactis, and Bifidobacterium longum, in a 375 mg probiotic blend, plus a 100 mg prebiotic fiber blend. Individual strain IDs and amounts per species are not specified, and we would rather tell you that plainly than leave you guessing.
Key takeaways
- Strains are specific cultures within a species; research is often strain specific.
- CFU counts live organisms; check when it was measured.
- Bigger CFU numbers are not automatically better.
- Prebiotics are fibers that feed beneficial gut bacteria.
- Store probiotics cool and dry, and take them consistently.
Frequently asked questions
What are probiotic strains?
A probiotic strain is a specific, identified culture within a species, usually shown as a code after the species name. For example, Lactobacillus acidophilus is a species, and a strain is one particular, traceable version of it. Research results are often tied to specific strains rather than whole species.
What does CFU mean on a probiotic?
CFU means colony forming units, an estimate of how many live microorganisms are in a serving. Check whether the count is guaranteed at time of manufacture or through expiration, because live counts naturally decline over time. A higher CFU number is not automatically more effective.
What is the difference between probiotics and prebiotics?
Probiotics are live beneficial microorganisms. Prebiotics are fibers your body cannot digest that feed the beneficial bacteria already in your gut. Some products combine both. Foods like onions, garlic, asparagus, bananas, and oats naturally contain prebiotic fibers.
Do probiotics need to be refrigerated?
Some do and some do not. Shelf-stable probiotics use dried cultures and protective packaging so they can be stored at room temperature. Follow the label, and keep any probiotic somewhere cool and dry with the lid closed, away from heat and humidity.
When is the best time to take a probiotic?
Follow your product label. Plum Probiotic 40 Billion suggests 1 capsule daily, preferably in the morning before food. Whatever time you choose, taking it consistently every day matters more than the exact timing.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.