How Probiotics Are Counted in CFU and AFU

I

A Number That Describes a Living Population

Most ingredients on a label are expressed by weight. Three hundred milligrams of a mineral is three hundred milligrams on the day it is made and, give or take, on the day it is opened. A probiotic does not behave that way. What it contains is a population of microorganisms, and a population is described by how many individuals it holds, not only by how much it weighs.

That is why probiotic labels carry a second kind of number. Alongside the milligrams, they state a count of cells, written in a unit that names the method used to count them. The two units met most often are the colony-forming unit, or CFU, and the active fluorescent unit, or AFU. They answer related questions in different ways, and reading them well starts with knowing what each one was built to measure.

The difference matters because counting living things is never as simple as counting objects. Cells can be active or dormant, single or clumped together, quick to grow in a laboratory or slow and demanding. Each counting method makes choices about which of those cells it can see. The Codeage guide to enzymes and probiotics in digestion sets out where probiotics sit in the broader picture; this article stays with the number itself.

Seen this way, a count is less a quantity than a method made visible. The unit tells the reader how the cells were counted, and the small print beside it tells the reader when.

II

The Colony on the Plate and What It Can See

The colony-forming unit is the long-established unit of microbiology. To arrive at it, a sample is diluted in steps and spread onto a nutrient medium in a dish, then incubated at a set temperature for a set time. Cells that can divide under those conditions multiply until each one becomes a visible colony. The colonies are counted, the dilution is factored back in, and the result is reported as colony-forming units.

The name is careful for a reason. A single colony may grow from one cell or from a small cluster that stayed together, so the unit counts the starting points of growth rather than individual cells. The method has a clear strength: a colony is direct evidence that something in the sample was alive and able to reproduce in the laboratory.

That same requirement defines its limits. A plate count sees only the cells able to grow on that medium, in that atmosphere, within that time. Cells that are alive but not dividing under those conditions, sometimes described as viable but non-culturable, do not form colonies and are not counted. Organisms that grow readily on a plate suit the method well, including the hardy spore formers described in the Codeage guide to soil-based organism probiotics.

For organisms that are fastidious, slow or sensitive to oxygen, the plate becomes a narrower window. The count still means something precise, but it describes what grew on the dish rather than everything that was in the sample.

III

Counting Cells One by One With Light

The active fluorescent unit comes from a different instrument. In flow cytometry, a sample is mixed with fluorescent dyes and passed in a narrow stream through a laser beam, one cell at a time. Each cell scatters the light and, depending on the dyes it has taken up, glows at particular wavelengths. Detectors record every event, and the instrument sorts them by the signals they give.

The dyes do the interpretive work. Some pass only through damaged membranes, others are converted into a fluorescent form by the enzymes of an active cell. Read together, they let the instrument distinguish cells that are intact and metabolically active from those that are not. The cells counted in the active group are reported as active fluorescent units. Because nothing needs to grow first, the method can see active cells that would not have formed a colony on a plate.

The approach has a formal basis. ISO 19344:2015, the international standard for counting lactic acid bacteria by flow cytometry, set out a method for counting active and total cells in starter cultures and probiotic dairy products. A review by Wilkinson, 2018, on flow cytometry and bacterial viability in probiotic products, in Trends in Food Science and Technology, compared the method with plate counting and discussed the staining and validation work it depends on.

Flow cytometry has its own choices to make. The dyes, the instrument settings and the way cells are gated all shape the final figure, which is why a count is always tied to a defined method. The two units do not convert into one another at a set ratio; each stands on its own procedure.

Studies referenced were conducted independently and did not involve any specific Codeage product.

IV

Why Akkermansia Is Counted This Way

Akkermansia muciniphila lives in the mucus layer that lines the colon, an environment with very little oxygen. Its original description in 2004 characterized it as strictly anaerobic and as an organism that grows on mucin, the glycoprotein that gives intestinal mucus its texture. Outside that setting, it is demanding to grow. It needs an oxygen-free atmosphere, specific nutrients and patience on the bench.

Those traits make a plate count a narrow view of an Akkermansia population. Cells exposed to small amounts of oxygen during handling, or simply slow to resume dividing, may be present and active without forming colonies in the time allowed. A method that counts active cells directly avoids that bottleneck, which is why the Akkermansia 500 Ultra label states its count in AFU.

Delivery is part of the same picture. An anaerobe in a capsule has to travel past the acidity of the stomach to reach the lower intestine where it naturally lives. An enteric coating is a capsule layer designed to resist dissolving in the stomach and to open further along the digestive tract. Akkermansia sits in Systemic Balance, the fourth pillar of The Longevity Code, the place the framework gives to the inner ecology of the gut and the body's systems.

V

What the Label Holds, Read Line by Line

The Supplement Facts panel of Akkermansia 500 Ultra is short. The serving size is one capsule, and the organism, its count and the footnote that dates it sit at the top of the panel, in the order set out above.

Beside the organism sits 276 mg of chicory inulin, a chain of fructose units that the human body does not digest on its own and that reaches the colon intact, where resident bacteria ferment it. Pairing the two follows the logic of a synbiotic, an organism and a fiber chosen to accompany it.

The other ingredients are hypromellose, which forms the vegetarian capsule, L-leucine, silica and the enteric coating. The jar holds 90 capsules, which at one capsule a serving is 90 servings.