You see the words “lactic acid bacteria” all the time on yogurt labels and supplement bottles.

We tend to think of lactic acid bacteria as a single type of microorganism. But the truth is quite different. “Lactic acid bacteria” is actually a broad name for a huge group containing many different types. And even within the same species, different strains can have very different characteristics.

When we talk about strains, we’re referring to individual variations within the same bacterial species — sort of like different people within the same community. Just as people from the same region can have different personalities and traits, so too can bacterial strains from the same species have slightly different properties.

A fascinating original research paper published in 2026 in the journal Frontiers in Microbiology took a detailed look at these differences from both functional and genetic angles. The study was conducted by researchers at Korea University in South Korea.

Today, I’d like to use this research as a window into the diversity that lies beneath the surface of that simple word: “lactic acid bacteria.”

Lactic Acid Bacteria Are Closer Than You Think

Lactic acid bacteria aren’t some exotic microorganism found only in specialized environments. The 27 strains studied in this research were all collected from ordinary places — the human mouth and everyday foods.

Lactic acid bacteria live in fermented foods like yogurt, pickles, and cheese, of course. But they’re also found in vegetables, dairy products, and even on the surface of our own bodies. While they all share a common trait — breaking down sugars to produce lactic acid — the variety of species and strains living around us is remarkably diverse.

That’s exactly why it makes sense to collect bacteria from various sources and compare their properties under identical conditions. You never know — a strain with completely unknown characteristics might be living right under your nose.

Gathering and Comparing 27 Lactic Acid Bacterial Strains

The research team collected 27 lactic acid bacterial strains from human mouths and food sources.

These included various strains such as Lactobacillus rhamnosus, L. casei, L. reuteri, and L. paracasei, along with Lactococcus lactis. The most common group turned out to be the rhamnosus family. These are all bacteria whose names you’ve probably seen on yogurt labels or supplement packages.

The team lined up these strains side by side under identical conditions and measured several key properties. By taking bacteria that have been studied separately and comparing them with the same measuring stick, the differences between strains become crystal clear.

The Differences Were Striking

The main properties investigated were these:

First, resistance to acid. Second, resistance to bile. When bacteria enter through the mouth, can they survive the stomach acid and the bile that flows into the intestines? This property is studied because it determines whether bacteria can pass through the digestive system alive.

The researchers also measured how well the strains adhered to intestinal cell models, and their antimicrobial activity — their ability to suppress the growth of other bacteria.

The results were unambiguous. These properties varied widely among the different strains. For example, when it came to adhesion, L. reuteri strains showed the highest values. Even though they all fall under the umbrella term “lactic acid bacteria,” each individual strain had its own strengths and its own unique characteristics.

What Do These Properties Actually Mean?

There’s a reason researchers focus on measuring these specific properties.

Resistance to acid and bile serves as a rough indicator of whether bacteria can survive the harsh environment of the stomach and intestines. If we want bacteria to reach the gut alive, they first have to be tough enough to get through the digestive tract intact. That’s the basic logic.

Adhesion property relates to how well bacteria can stick around inside the gut. Antimicrobial activity is noted because it suggests bacteria might suppress the growth of unwanted microorganisms as they compete in the intestinal environment.

But here’s something important to understand: all of these are properties measured in laboratory conditions or using cellular models. Just because a strain shows high values for a particular property doesn’t mean it will automatically deliver health benefits when eaten. These measurements are really just a starting point — preliminary indicators to help researchers identify promising candidates.

What the Genome Reveals

So where do these differences in properties come from? The research team also analyzed the genetic makeup — the genome — of the bacteria.

What they found was fascinating. Some bacterial strains had more copies of genes involved in remodeling cell walls, finishing proteins on the cell surface, and producing enzymes that break down the bacteria’s own cells (genes like galE, lgt, and ftsW were highlighted).

When it came to antimicrobial activity, researchers found connections between this property and specific gene clusters that code for antimicrobial compounds.

In other words, the differences in properties between strains have a genetic foundation. Even if bacteria look identical on the surface, differences in their genetic blueprints translate into different capabilities. By connecting what bacteria can do in observable terms with the genetic architecture underneath, we gain a more complete understanding. That’s what genome analysis is really about.

Why Looking at the Strain Level Matters

What this research teaches us is the importance of understanding lactic acid bacteria at the strain level.

Just because a product says “contains lactic acid bacteria,” you can’t tell from the name alone which strain is in there or what properties it has. Even bacteria of the same species can differ dramatically in acid tolerance or how readily they stick to gut cells — depending on the strain.

That’s why in the research world, bacteria aren’t identified just by species name. Scientists drill down to the strain level, pinpointing exactly which strain they’re working with and then carefully testing each one’s properties. Research like this, where many strains are compared under identical conditions, forms the foundation for that detailed investigative work.

This perspective also shapes how we should think about choosing products. Rather than making decisions based solely on words like “lactic acid bacteria” or “contains ○○ strain,” it’s worth paying attention to which specific strain is being used and what evidence supports that choice. The lesson here is to not be dazzled by flashy marketing language, but to read the information thoughtfully and carefully.

We’re Still in the “Candidate” Stage

I want to be very clear about this point.

The properties measured in this study — acid resistance, adhesion, antimicrobial activity — are things researchers look at when selecting candidate strains for potential probiotic use. But these are measurements taken in test tubes and cell models. They don’t prove that eating these bacteria will actually produce health benefits in people.

Even if researchers identify a strain with promising properties, they still need to verify whether it actually helps people, whether it’s safe, and how much would be needed — all in actual human studies. A “candidate” is just that — a candidate. It’s important to keep potential possibilities separate from facts confirmed in human research.

One Step in a Longer Journey

This research didn’t reveal some dramatic health breakthrough. Rather, it’s the accumulation of patient, methodical work: gathering many strains, measuring their properties under controlled conditions, and connecting those findings to genetic data. This kind of steady groundwork is what builds toward reliable knowledge down the road.

Which strains have which properties? What genes underlie those properties? As this basic map gradually expands, researchers get better at predicting which strains to investigate next and how to investigate them. It’s not flashy, but this step-by-step progress is exactly what moves our understanding of fermentation and bacteria forward.

What Lies Beneath a Simple Label

The word “lactic acid bacteria” is conveniently broad, grouping many microorganisms under one umbrella. But in that convenience, we easily overlook the individual character of each strain.

Yet look closer, and you’ll find remarkable diversity. There are strains tough against acid, strains that cling readily to gut walls, strains that hold back unwanted bacteria. Each one possesses its own unique properties and its own story.

The next time you come across the words “lactic acid bacteria,” try pausing for a moment to imagine the vast landscape of individual differences hidden beneath that simple phrase.

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Within a single, all-encompassing name lies an uncountable wealth of individual character.

※ This article is based on personal experience and publicly available information. It is not intended to diagnose, treat, or prevent any disease. If you have health concerns, please consult a doctor or registered dietitian. See our Disclaimer.