The Hidden Passports of Microbes

How Scientists Keep Track of the Bacteria That Make Our Yoghurt and Kefir and Keep Us Healthy

L.Bulgaricus

If you’ve ever read the back of a probiotic supplement pack, you’ve probably seen long, complicated names like Lactobacillus bulgaricus, Streptococcus thermophilus, or Bifidobacterium longum.

Sometimes there’s even a strange number next to them — something like NBIMCC 8244 or DSM 17938. Those codes may look like random lab jargon, but they’re actually the hidden passports of microbes or something like their ID cards. They help scientists know exactly which living strain is being used and where it came from.

What’s a “strain”?

All dogs belong to the same species, "Canis familiaris," but a Chihuahua and a German Shepherd are very different. Bacteria are like that, too. Two microbes may share the same name, yet behave quite differently depending on their lineage. That’s why scientists use the word strain — it means a particular version of a species, with its own features and personality. For example, every Lactobacillus bulgaricus strain can make yoghurt, but some give a thicker texture, others a tangier flavour, and others survive better in the gut. Strain identity really matters — not all members of one species do the same job.

Why do bacteria have strain numbers?

When a scientist isolates a new bacterium — perhaps from milk, plants, or a human source- they send it to a microorganism bank, a place that works like a library for microbes. Each culture is stored in a tiny frozen or freeze-dried tube and given a unique strain number — its permanent identity tag. For example:

- Lactobacillus bulgaricus NBIMCC 8244

- Streptococcus thermophilus NBIMCC 8253The letters tell you which “library” it’s kept in:

- DSMZ – German Collection of Microorganisms and Cell Cultures

- ATCC – American Type Culture Collection

- JCM – Japanese Collection of Microorganisms. When researchers or food producers need a specific microbe, they can order it by number, like borrowing a precise book from a global catalogue.

- NBIMCC – National Bank for Industrial Microorganisms and Cell Cultures (Bulgaria)

“Belonging to” vs. “similar to”

Sometimes scientific documents say that one strain “belongs to” another, or is “similar to” it. This isn’t just a language quirk — it shows how closely related different cultures are.

• Belonging to (or equivalent to) means it’s the same isolate kept in more than one collection. A bacterium first deposited in Bulgaria might later be sent to Germany and get a new DSM number — but it’s still the same strain.

• Similar to means it’s a different isolate of the same species. These bacteria share many traits and act alike, but they’re not identical — more like cousins than twins. This difference matters. If two cultures are genuinely the same strain, safety and performance data for one can apply to the other. If they’re only similar, they need their own testing.

Why strain numbers matter

Strain numbers aren’t just technical details. They guarantee that the bacteria used in food and probiotics are authentic, safe, and consistent. Without them, nobody could be sure which microorganism is inside a starter or supplement.

Strain codes ensure:

- Traceability – we know where the culture came from.

- Consistency – every batch uses the same organism.

- Safety – only food-grade, approved strains are used.

The European Food Safety Authority (EFSA) keeps a Qualified Presumption of Safety list for microorganisms with a long history of safe use — including Lactobacillus, Bifidobacterium, and Streptococcus thermophilus. In the US, similar strains are listed as GRAS (Generally Recognised as Safe).

The role of NBIMCC strains

The NBIMCC, based in Sofia, Bulgaria, maintains a rich collection of traditional and modern microbial strains used in yoghurt, kefir, and other fermented foods. Some examples include:

- Lactobacillus delbrueckii ssp. bulgaricus NBIMCC 8244

- Streptococcus thermophilus NBIMCC 8253

- Lactobacillus reuteri NBIMCC 8777

These cultures are part of the country’s long tradition in dairy fermentation and have been evaluated by scientists for their safety and beneficial properties. They’re food-grade, non-pathogenic, and used in starter cultures across Europe and beyond.

A simple way to think about it

Imagine two bakers making sourdough bread. One uses a piece of the original starter passed down for generations — that’s the same strain. The other creates a similar starter from scratch — that’s a similar strain. Both bake good bread, but only one has the exact “family line” of microbes. It’s the same for bacteria. Strain numbers make sure that what scientists or producers use today is the same trusted culture from yesterday.

A worldwide network of microbial libraries

Across the planet, hundreds of collections work together to preserve microorganisms — from the US and Japan to Germany and Bulgaria. They share information through the World Federation for Culture Collections (WFCC), ensuring that beneficial microbes remain accessible, traceable, and safe for generations to come. Each tiny tube stored in a freezer represents more than a cell culture — it’s a piece of scientific heritage, a time capsule of life.

Why commercial yogurts rarely show strain numbers

Most yogurts you see in shops don’t list the exact bacterial strain numbers on the jar — and there’s actually a good reason for that.

When we talk about “strains,” we mean specific genetic versions of a bacterium, each registered in a microbial collection with its own ID number, like Lactobacillus bulgaricus NBIMCC 8245 or Lactobacillus reuteri DSM 17938. These numbers are mainly used in science to make sure everyone’s talking about the same organism, since even within one species, different strains can behave quite differently.

However, food labelling laws don’t require yogurt producers to go into that level of detail. They only have to say which species of bacteria are present — for example, Lactobacillus bulgaricus and Streptococcus thermophilus — the two classic yogurt starters.

Listing the strain numbers is only necessary for probiotic products that make a specific health claim, like “supports digestion” or “improves gut flora,” because those claims must be based on clinical studies tied to exact strains.

There’s also a commercial side to it. Most yogurt companies use their own starter blends, developed over many years, to achieve the right taste, texture, and aroma. The exact strains are part of their trade secrets, so they keep them confidential.

On top of that, industrial yogurts often use a mix of several strains working together, and the blend might change slightly over time, which would make detailed labelling confusing and complicated to keep consistent.

You’ll only see strain numbers on certain probiotic drinks or supplements — things like Yakult (L. casei Shirota) or Activia (Bifidobacterium animalis subsp. lactis BB-12) — because those products are based on specific, well-researched strains with proven health effects.

In short, yogurts don’t list strain numbers simply because they don’t have to, and because those details are more relevant to scientists and probiotic manufacturers than to everyday consumers. What matters most for regular yogurt is that it’s made with live, active cultures — even if the exact strain remains behind the scenes.

The bottom line

Those cryptic codes on yoghurt labels or scientific papers aren’t random. They’re part of an international system that keeps our food, medicine, and research reliable.

So next time you open a pot of yoghurt, remember: inside are millions of helpful little microbes, each with its own passport, safely stored and recorded in a global library of life.