Myth #2: All CFU are alike
Microbial numbers are generally expressed in terms of Colony Forming Units (CFU).
A sample of a microbial product/culture is put through a series of dilutions with a bit of each dilution smeared on a petri dish with an appropriate nutrient. These are then incubated for a specified period of time. They are then examined, and by counting the colonies, the dots of microbes that appear. After applying some statistics, a rough approximation of the number of microbes present may be calculated.
On many probiotic products, this number is reported as if it is very specific and precise. It is nothing of the sort. At best, serial dilutions can tell you what order of magnitude of microbes were present but if the same test is run on the same sample, the CFU ‘count’ can vary.
One reason for this variability is the fact that a colony, a dot on a petri dish that is counted as a single unit, can represent very different things. It is possible for a single cell to develop into a colony, but it is more probable that a colony developed from a clump of cells.
Some products, especially fresh, live products, tend to produce large clumps of cells rather than individual cells swimming about on their own. Thus, a CFU count from a fresh product could represent something very different to a CFU count of a freeze-dried powder that does not contain large clumps of microbes. It is important to keep this in mind when reading labels with enormous CFU counts on them.
Next week myth #3
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