HOW TAXONOMY HELPS US UNDERSTAND PROBIOTICS (and why the PRL2020 strain of Bifidobacterium breve is not “just any” strain)
When we talk about probiotics, we often come across long names: Bifidobacterium breve PRL2020, Lactobacillus something, acronyms, codes.
In reality, these are valuable pieces of information: they represent the microorganism’s scientific identity card, essential for understanding its real characteristics. Without that “ID card,” it would be like talking about a person without knowing their name, surname, or origin.
To understand why these names matter so much, we need to take a step back and look at the science that brings order to the living world: taxonomy, the system that classifies organisms into increasingly specific groups.
The same principle applies in microbiology and, consequently, in the world of probiotics.
The roots of classification: from Aristotle to Linnaeus
The need to bring order to biodiversity is not new. As early as the 4th century BCE, Aristotle proposed the first major distinction between animals and plants, based on observable characteristics.
However, it was not until the 18th century that a more rigorous classification system emerged. Carl Linnaeus (Carl von Linné), a Swedish naturalist, developed a systematic method and introduced binomial nomenclature, which is still used worldwide today.
In his Systema Naturae (1758), Linnaeus established that each species should be identified by two terms:
- the genus (the scientific “surname”),
- the species (the “given name”).
In binomial nomenclature, genus and species are always written in italics, with the genus capitalized and the species in lowercase.
Correct examples include Panthera tigris (tiger) or Helianthus annuus (sunflower).
This uniformity avoids confusion and allows scientists to communicate precisely anywhere in the world.
From systematics to modern taxonomy
Taxonomy (from the Greek taxis, “order,” and nomos, “law”) is the discipline that groups living beings based on their evolutionary and structural relationships.
Taxonomic groups—also called taxa (singular taxon)—are the categories used to organize organisms.
Traditionally, classification includes eight levels:
Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species
With the advent of genetic sequencing techniques, many modern classifications propose an initial division into two major domains:
- Bacteria
- Archaea
Eukaryotes—organisms with nucleated cells (protists, fungi, plants, animals, and humans)—form another major grouping.
When discussing probiotics, the most relevant domain is clearly Bacteria, which includes the microorganisms that make up the human microbiota.
Getting closer to probiotics: the levels that really matter
Although there are many taxonomic levels, when it comes to probiotics we are mainly interested in the last four:
- Family
- Genus
- Species
- Strain (the most specific level)
We can imagine these levels as nested boxes: each step narrows the field and increases precision in identifying the microorganism.
Family, genus, species: the biological identity of a bacterium
Let’s take the case of Bifidobacterium breve PRL2020, the key strain in Brevicillin®:
- Family: Bifidobacteriaceae – groups bacteria that share structural and functional characteristics.
- Genus: Bifidobacterium – a fundamental genus of the human microbiota, especially prominent in early life and still important in adulthood.
- Species: Bifidobacterium breve – one of the most studied species, known for its presence in the infant gut and its probiotic potential.
Knowing the species is helpful, but it is not enough to understand how a specific bacterium will behave in the body.
To reach its full identity, we need one more level.
The strain: the detail that changes everything
A strain is a bacterial population derived from a single isolate. It is highly homogeneous (clonal) and possesses unique genetic and functional characteristics.
As a result:
- two strains of the same species can have different effects;
- two products labeled Bifidobacterium breve may contain very different microorganisms;
- making an informed choice about a probiotic requires knowing the strain, not just the species.
To visualize the concept:
- all dogs belong to the same species, Canis lupus familiaris;
- within the species, there are different breeds with distinct appearances and behaviors.
In the same way:
- the species Bifidobacterium breve represents a broad group;
the PRL2020 strain is a much more specific subset.
🔎 Scientific disclaimer
This example is useful but should be interpreted correctly:
- a dog breed is not a strain;
- within breeds, there is considerable variability between individuals;
- in bacteria, a strain is extremely homogeneous and of clonal origin, because it derives from a single progenitor.
The metaphor simply helps clarify the general logic:
Species = large container.
Strain = small, well-defined group with distinctive features.
Why the strain truly matters in probiotics
Differences between strains can involve crucial aspects such as:
- survival during gastric transit;
- ability to adhere to the intestinal mucosa;
- production of beneficial metabolites;
- interaction with the immune system;
- sensitivity or resistance to antibiotics.
These properties do not belong to the species as a whole, but to the specific strain.
This does not mean that the genus is unimportant. On the contrary, the genus Bifidobacterium has characteristics that make it naturally suited to life in the human gut and to playing a beneficial role in the microbiota, particularly in infants.
The genus defines the bacterium’s “vocation,” while the strain determines its most specific behaviors.
Focus: the taxonomic identity of Bifidobacterium breve PRL2020
🧬 Family: Bifidobacteriaceae
🧬 Genus: Bifidobacterium
🧬 Species: Bifidobacterium breve
🧬 Strain: PRL2020
PRL2020 is a strain that is:
- uniquely genetically typed;
- selected for stable, reproducible characteristics over time;
- studied for its ability to coexist with specific β-lactam antibiotics;
- safe, as it is not associated with transferable resistance genes.
It is a strain designed to support microbiota balance at times of greatest vulnerability: during and after antibiotic therapy.
Why this distinction really helps in making a choice
Brevicillin® does not contain a generic Bifidobacterium breve, but that specific Bifidobacterium breve: PRL2020.
This makes it possible to link:
👉 label name → strain identity → expected benefit
And this is how taxonomy stops being an abstract concept and becomes a practical tool for choosing a probiotic in an informed and conscious way.
* Biasucci, G.; Capra, M.E.; Giudice, A.; Monopoli, D.; Stanyevic, B.; Rotondo, R.; Mucci, A.; Neglia, C.; Campana, B.; Esposito, S. Use of Probiotics During Antibiotic Therapy in Pediatrics: A Cross-Sectional Survey of Italian Primary Care Pediatricians. Antibiotics 2025, 14, 577. https://doi.org/10.3390/antibiotics14060577