About this article: This article introduces foundational laboratory research on lactic acid bacteria. It does not demonstrate that any particular food or bacterium can prevent or treat disease. The experiments described were conducted on agar plates and have not been confirmed to occur the same way in the human body. The strains obtained in the research have not undergone genetic analysis for species identification—they remain at the stage of “presumed lactic acid bacteria”—and their safety has not been established. Regarding antimicrobial activity, the specific compounds responsible have not been identified. Additionally, the mention of raw milk in this article is not intended to recommend consuming it as-is (food safety considerations are explained in the text).

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Where do the lactic acid bacteria that make yogurt and cheese actually come from?

In factories, starter cultures use bacteria that have been carefully selected beforehand. But throughout the world, traditional fermented milk products have relied on bacteria that come from the local milk and environment of their regions.

A research study examining these “local lactic acid bacteria” was published in the academic journal Scientific Reports in 2026. It comes from a research team at Debre Tabor University and Gondar University in Ethiopia.

Today, let’s use this research as a window into the beginning of scientific work—how we “search for and examine” lactic acid bacteria.

From 25 Samples, 20 Isolates Were Obtained

The work the research team carried out was methodical and painstaking.

They collected 25 samples—a combination of fermented milk and raw milk—from the Gondar region in northern and southern Ethiopia. Using growth media specifically suited for cultivating lactic acid bacteria (MRS agar medium), they obtained 20 isolates presumed to be lactic acid bacteria from those 25 samples.

What’s important here is that these isolates remain at the “presumed” stage. They were identified as lactic acid bacteria based on observable characteristics and biochemical properties, but they have not undergone genetic analysis for species identification. In this article, I’ll refer to them as “presumed lactic acid bacteria isolates.”

These isolates were then tested for various properties: tolerance to pH levels, tolerance to salt concentration, and tolerance to temperature. Specifically, they examined growth under pH conditions of 3, 7, and 9; salt concentrations of 2%, 4%, and 6%; and temperatures of 15°C, 37°C, and 45°C.

Examining these properties provides clues about potential applications in food manufacturing and preliminary information about tolerance to some conditions found in the digestive tract. However, testing alone cannot determine whether bacteria can survive passage through the human digestive system. This is because the test doesn’t involve a comprehensive digestive tract model that includes bile acids and digestive enzymes.

Still, possessing these properties only means the bacteria could be “candidate organisms”—nothing more. I’ll come back to this important point later.

What Was Discovered

Let me share some of the reported findings.

First, all the isolated strains showed “gamma hemolysis.” This means they showed no activity that would destroy red blood cells—an important first checkpoint when considering safety.

The amount of lactic acid produced ranged from 5.0% to 8.2%. Additionally, several strains were able to coagulate milk within 12 hours. The ability to coagulate milk is helpful when considering potential applications in fermented dairy products.

Different strains showed variation in these properties. Even bacteria isolated through the same process each had their own individual characteristics—a fact confirmed once again here.

”Antimicrobial Activity” Observed on Agar Plates

What drew particular attention in this research was antimicrobial activity.

Small wells were made in agar plates, liquid was added to them, and researchers observed how much bacteria in the surrounding area would struggle to grow. This is called the “agar well diffusion method”—a traditional approach used for many years. The size of the zone where growth was inhibited (the inhibition zone) was measured.

According to the paper’s abstract, inhibition zones were reported as 15–27 mm against Staphylococcus aureus, 8–13 mm against E. coli, 10–17 mm against Pseudomonas aeruginosa, and 8–14 mm against Salmonella typhi.

Here’s a crucial methodological detail: the test used not the bacteria themselves, but the culture supernatant—the liquid left after the bacterial cells were removed. Moreover, the supernatant was not treated to neutralize its acidity or to break down proteins. This means the inhibition zones could have resulted from acidification by lactic acid and other compounds, hydrogen peroxide, and various other metabolic byproducts—but which specific component was responsible cannot be determined. No specific antimicrobial compound or bacteriocin activity was confirmed.

And remember: this is an experiment conducted on agar plates. It has not been verified that the same thing happens in food or inside the human body. This absolutely does not mean that eating lactic acid bacteria would eliminate food poisoning pathogens.

The properties observed in the laboratory are, at most, “clues for selecting candidates”—nothing beyond that.

It is well-known that acids produced by lactic acid bacteria can affect the growth of other microorganisms in food. However, we cannot directly judge food preservation or safety from the results on agar plates shown here. It’s essential not to confuse these different matters.

Limitations Clearly Stated by the Research Team Itself

One of the honest points about this research is how clearly its limitations are articulated.

The paper explicitly states that species-level identification and safety evaluation remain “presumptive.” In other words, which specific species these isolated bacteria belong to, and whether they can be used safely, has not yet been confirmed.

Beyond that, the team notes that detailed genetic analysis (molecular characterization), comprehensive in vitro testing, and animal studies would be necessary to investigate the potential of these organisms as probiotics and their applications in industry.

Additionally, some tests did not preserve individual data from repeated measurements, and standard deviations or error ranges were not provided. This is another reason to read the results with care.

Even when promising results appear, the research doesn’t stop there—it points to what should be investigated next. That’s what foundational research is: the accumulated building blocks of careful inquiry.

Antibiotic Sensitivity Was Also Examined

One more thing reported was the response to antibiotics.

While many of the isolates showed resistance to vancomycin and gentamicin, high sensitivity was reported to bacitracin, ampicillin, tetracycline, and penicillin. However, whether resistance genes are present or whether they could spread to other bacteria was not investigated.

There’s a reason these properties are examined. We want to avoid bacteria used in food having undesirable resistance traits that might spread to other organisms. When evaluating probiotic candidates, it’s standard practice to confirm such points from a safety perspective.

This research shows that these basic safety checks were indeed performed.

A Note About Raw Milk

In this research, raw milk (milk that has not been heat-pasteurized) was used as a sample.

Using something as research material and consuming it daily are entirely different matters. Raw milk can potentially contain bacteria that cause food poisoning. In Japan, when raw milk is used in food manufacturing, pasteurization under certain minimum conditions is required as a principle, and unpasteurized “special milk” is subject to exceptionally strict requirements. Casually drinking milk that hasn’t been heat-pasteurized is not recommended.

This article does not encourage drinking raw milk. Please understand the context: in a research setting, it was used as a material for searching for bacteria.

The Meaning of Steady, Patient Research

This research does not report dramatic discoveries. It collects bacteria from milk in a certain region of the world, measures their properties one by one, and organizes what should be investigated next. It’s unglamorous and time-consuming work.

But without the accumulation of such basic research, we would have no new fermented foods or safe bacteria to use. The fact that fermented foods and their bacteria are being studied in locations around the world speaks to how widely the practice of fermentation has spread.

Ethiopia has its own traditional culture of fermented milk. Just as Japan has miso and pickles, each region has its own forms of fermentation that have developed over time. And within those traditions, there are likely many bacteria that have never been thoroughly studied.

Research like this is also a first step in shining a light on such unknown organisms. The movement to view the world’s fermented foods as “treasure troves of bacteria” has been spreading in various places in recent years.

Behind the yogurt and fermented milk we consume daily lies the history of such patient research. Next time you take a bite, I hope you’ll pause to think a little about the long journey of discovery behind it.

From Toshi

When I first read this research, what struck me most was how fascinating it is that the world of fermented foods still contains countless microorganisms whose names we don’t even know yet.

When we think of lactic acid bacteria used in yogurt and cheese, we tend to imagine bacteria that are carefully managed in factories, whose properties are well understood. But if we trace the history of fermentation back, humans have been harnessing the power of microorganisms in their local milk and environment since ancient times—long before we knew the names or genes of these bacteria.

This research, which searched for bacteria in Ethiopian raw and fermented milk, allows us to feel that original spirit of fermentation.

The research team collected 25 milk samples and obtained 20 isolates presumed to be lactic acid bacteria. They then examined each one individually—their appearance, biochemical properties, tolerance to acidity, salt and temperature, and the speed at which they could coagulate milk.

However, these 20 strains are not lactic acid bacteria whose species have been definitively confirmed through genetic analysis. They are “isolates presumed to be lactic acid bacteria” based on morphological and biochemical tests.

This distinction is often overlooked in general articles, but I think it’s very important. There’s a difference between saying “lactic acid bacteria were found” and saying “bacteria presumed to be lactic acid bacteria were isolated.” The difference reflects where the research has actually arrived.

In science, avoiding premature conclusions about things we don’t yet understand is also important work. This research is at the stage where bacterial exploration has begun—it has not reached the goal.

It’s also interesting that they tested whether the bacteria could grow under pH 3 conditions and in different salt concentrations and temperatures. These experiments provide clues for considering potential applications in fermented foods and whether the bacteria can tolerate some digestive tract conditions.

However, we cannot conclude from these results alone that “bacteria will survive passage through the human stomach.” The actual digestive tract contains not just stomach acid, but bile acids, digestive enzymes, food, other microorganisms, and many other factors.

There are several confirmatory stages between surviving specific conditions in a test tube and actually surviving in the human body while potentially providing health benefits.

I want to approach the term “probiotic candidate” carefully as well.

Probiotics are, by definition, live microorganisms that, when consumed in appropriate amounts, have been confirmed to provide health benefits to the host. These bacteria have not yet been confirmed as probiotics with health effects. They are merely “candidates” for future research.

The same applies to the finding of gamma hemolysis. Under the test conditions used this time, the bacteria showed no hemolytic activity that would destroy red blood cells—a result that becomes one piece of information in investigating safety.

However, the absence of hemolysis doesn’t definitively confirm that the bacteria are safe. There remain questions about the presence of genes related to toxicity, the possibility of antibiotic resistance genes spreading to other bacteria, and what happens when animals or humans actually consume them.

What particularly impressed me was the “antimicrobial activity” observed on agar plates.

When we hear that growth was inhibited around areas containing Staphylococcus aureus or E. coli, it’s natural to hope that “eating these lactic acid bacteria would eliminate disease-causing bacteria in the body.”

But what was used here wasn’t the lactic acid bacteria themselves—it was the culture supernatant with the bacterial cells removed. Moreover, that supernatant was not pH-neutralized.

Because lactic acid bacteria produce lactic acid, the culture medium becomes acidic. The suppression of pathogenic bacteria growth might have been simply due to the acidic environment. Hydrogen peroxide or other metabolic products could have been involved.

Since the pH-neutralization test and protein-degrading enzyme treatment weren’t performed, we cannot identify what actually created the inhibition zones. No special bacteriocin was discovered.

When you properly understand this, you realize that you cannot simply connect the strong-sounding word “antimicrobial activity” directly to health benefits.

That bacteria struggled to grow in a test tube is different from food being safer, which is different again from preventing or treating human infections. The appropriate way to understand these results is as clues for selecting isolates to study in greater detail.

The same applies to antibiotic response—you cannot simply say “resistance is dangerous” or “sensitivity is safe.”

Many isolates showed resistance tendencies to vancomycin and gentamicin, but genetic analysis is needed to determine whether this is an inherent trait unlikely to transfer to other bacteria, or whether it results from transferable resistance genes.

For bacteria intended for food use, this distinction is extremely important. The research team’s identification of molecular-level analysis and comprehensive safety evaluation as future tasks reflects this necessity.

It’s also important to note that some tests did not preserve individual data from repeated measurements and did not show standard deviations or error ranges. Even when numbers are presented, if we don’t know the degree of variation in those numbers, we may not be able to adequately judge the reliability of the results.

Writing about these limitations doesn’t diminish the value of the research. Distinguishing between what we understand and what we don’t yet understand is essential for moving forward to the next stage of research.

I also want to be clear about raw milk so there’s no misunderstanding.

In this research, raw milk was used as a research sample for searching for bacteria. This does not mean that consuming unpasteurized milk is beneficial to health.

Raw milk may contain diverse microorganisms, but it may also contain bacteria that cause food poisoning. What researchers do when isolating bacteria under controlled laboratory conditions is entirely different from someone consuming unpasteurized milk at home.

We shouldn’t take food safety risks lightly just because of the possibility that “rare bacteria might be present.” Being a traditional food or naturally occurring doesn’t automatically guarantee safety.

And yet, I find a quiet appeal in research like this.

Isolating bacteria from Ethiopian milk, numbering them, growing them on media, recording their properties one by one. That work might not make headline news. But new fermented foods and safe starter cultures cannot be born without this kind of patient exploration.

Japan has its own fermentation culture—miso, soy sauce, pickles, sake—developed alongside the microorganisms of its regions. Ethiopia has its fermented milk, passed down through its climate and way of life.

Though the countries and foods are different, there’s a common thread: humans have used the power of microorganisms to preserve food and make it delicious. Scientifically studying a region’s fermented foods isn’t just about finding useful bacteria—it’s also about documenting regional food culture, isn’t it?

Whether the bacteria found this time will actually be used in food products someday remains unknown. Many bacteria will fail safety verification and never reach practical application.

Yet by gradually shining light on the unknown, narrowing down candidates, and passing them forward to the next stage of research, we advance fermentation science.

Rather than quickly concluding that we’ve found a “bacteria good for the body,” treating bacteria whose names aren’t even confirmed as future subjects of study, handling them with care—I want to cherish that kind of caution.

The future of fermentation isn’t built on major discoveries alone. It’s shaped gradually, step by small step: growing a single bacterium on a petri dish, examining its properties, repeating this work over and over, with patience and precision.

※The image in this article is a conceptual image representing fermented milk and lactic acid bacteria research. It is not a photograph of the actual samples or specific products used in the study.

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Unglamorous as it may be, examining bacteria one by one sustains the future of fermentation.

※ 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.