Brevibacterium casei is one of the most influential bacteria on the surface of ripened cheeses, often becoming the single most abundant organism by the time a wheel reaches maturity. In one meta-omics study of a surface-ripened cheese community, it accounted for roughly 71% of all bacterial sequence reads by day 31 of ripening. Despite living in the shadow of its more famous relative Brevibacterium linens, long considered the archetype of smear-cheese bacteria, B. casei plays a distinct and arguably larger role in many cheeses than the textbooks suggest. Its biology reaches well beyond the cheese cave, touching human skin ecology, salt-tolerance research, and even potential therapeutic applications.
Origins and Classification
Brevibacterium casei was formally described as a new species in the early 1980s, when researchers used DNA base composition studies and DNA-DNA hybridization to sort out a confusing group of coryneform bacteria isolated from dairy products and human skin. The dairy isolates, collected from cheese and milk, were designated Brevibacterium casei, while related strains from human skin became Brevibacterium epidermidis.1Elsevier. Brevibacterium casei sp. nov. and Brevibacterium epidermidis sp. nov. Before that formal split, many cheese-surface isolates had been lumped under the catch-all label “Brevibacterium linens,” which made it look as though a single species dominated the rind. Modern molecular identification has revealed that B. casei is actually more prevalent on many cheese surfaces than B. linens, a finding that reshuffled the understanding of smear-cheese microbiology.
How It Arrives and Takes Over the Rind
Surface-ripened cheeses go through a predictable microbial relay. In the earliest days of ripening, yeasts such as Debaryomyces hansenii and Geotrichum candidum dominate the rind. These yeasts metabolize lactic acid produced during curdling, which raises the surface pH from an acidic environment that most bacteria cannot tolerate to one that is closer to neutral. Once the pH climbs high enough, bacterial species move in and gradually overtake the yeasts.2PubMed Central. Omics-Based Insights into Flavor Development and Microbial Succession within Surface-Ripened Cheese B. casei is among the bacteria that thrive in this second wave. In Fontina PDO cheese, for example, it has been detected on the maturing surface from about one week through four weeks of ripening, alongside Arthrobacter nicotianae and Corynebacterium glutamicum.3Journal of Applied Microbiology. Maturing dynamics of surface microflora in Fontina PDO cheese studied by culture‐dependent and ‐independent methods
What makes B. casei so competitive in this environment? A large part of the answer is its metabolism. Studies of surface-ripened cheese bacteria have shown that coryneform species like B. casei (referred to in some older literature as Corynebacterium casei) readily consume lactate as a primary energy source. They cannot use lactose, the sugar in milk, but by the time they colonize the rind, lactose has already been consumed by lactic acid bacteria during the initial fermentation. Lactate, the byproduct of that fermentation, is exactly what B. casei thrives on. The organism also draws energy from several amino acids, with glutamate, proline, serine, and lactate all capable of restarting its growth after it exhausts its initial nutrients.4American Society for Microbiology (Applied and Environmental Microbiology). Growth characteristics of Brevibacterium, Corynebacterium, Microbacterium, and Staphylococcus spp. isolated from surface-ripened cheese This metabolic flexibility helps explain why B. casei can keep growing even as the chemical landscape of the cheese surface shifts throughout ripening.
What B. Casei Actually Does to Cheese Flavor
The flavors and aromas of washed-rind and smear-ripened cheeses are famously pungent. B. casei contributes to this character in several ways. By breaking down amino acids on the rind surface, it produces volatile sulfur compounds, ammonia, and other small molecules that give cheeses like Limburger, Époisses, and Reblochon their funky, sometimes foot-like smell. The proteolytic activity of Brevibacterium species in general is well documented, and B. casei specifically has been shown to produce enzymes capable of hydrolyzing proteins into peptides and free amino acids, which then serve as precursors for aroma compounds.
In a meta-omics study that tracked a surface-ripened cheese community over its entire ripening cycle, B. casei emerged as the dominant bacterium by the end of the process, reaching roughly a billion colony-forming units per gram of cheese.5PLOS ONE. Overview of a Surface-Ripened Cheese Community Functioning by Meta-Omics Analyses At that density, its metabolic output overwhelms most other organisms on the rind, and its biochemical fingerprint essentially becomes the cheese’s flavor signature in the final product. The species is not just a passenger; it is the engine of late-stage surface ripening in many cheese varieties.
Genomic Adaptations to the Cheese Environment
Comparative genomics has given researchers a clearer picture of why certain Brevibacterium species succeed in cheese while others do not. A study comparing the genomes of 23 Brevibacterium strains, twelve of which were isolated from cheeses, found that cheese-adapted strains carry distinctive gene clusters related to salt tolerance, iron acquisition, and the ability to metabolize the specific energy compounds available on a cheese surface.6PubMed Central. Comparative genomic analysis of Brevibacterium strains: insights into key genetic determinants involved in adaptation to the cheese habitat Salt tolerance is particularly relevant because smear cheeses are regularly washed with brine during ripening, creating a surface environment with salt concentrations that many bacteria cannot handle.
B. casei’s resilience in salty conditions extends beyond the cheese cave. One strain, B. casei G20, isolated as an endosymbiont of beetles living in arid and semi-arid habitats, was found to tolerate sodium chloride concentrations up to 11%. Metabolic profiling of that strain during growth revealed differential production of benzene compounds and organic acids, suggesting biochemical strategies for coping with osmotic stress.7PubMed Central. Diversity and saline-alkali resistance of Coleoptera endosymbiont bacteria in arid and semi-arid climate The fact that B. casei can tolerate such harsh conditions outside of dairy settings hints that its salt-tolerant machinery evolved for reasons unrelated to cheese, and cheesemakers have simply been exploiting those pre-existing capabilities.
Another genomic feature of interest is a putative histamine catabolism pathway identified in Brevibacterium strains from Austrian hard cheeses, with homologs of the relevant gene cluster also found in B. casei CIP 102111.8Scientific Reports. Brevibacterium from Austrian hard cheese harbor a putative histamine catabolism pathway and a plasmid for adaptation to the cheese environment Histamine accumulation in fermented foods is a real concern for people with histamine intolerance, so the possibility that certain Brevibacterium strains can actually break histamine down during ripening is a notable finding. Growth experiments confirmed that Brevibacterium strains harboring this pathway can use histamine as a sole carbon source, growing to meaningful cell densities on it before entering stationary phase.8Scientific Reports. Brevibacterium from Austrian hard cheese harbor a putative histamine catabolism pathway and a plasmid for adaptation to the cheese environment Whether this translates to meaningfully lower histamine levels in finished cheese is still being investigated, but the genetic and experimental evidence is promising.
Antimicrobial Properties and Food Safety
Brevibacterium species produce a surprising variety of bioactive compounds. A comparative genomic analysis of biosynthetic gene clusters across the genus found that some strains can synthesize antimicrobial molecules, including phenazine derivatives. One strain, H-BE7, showed antibacterial activity against both Salmonella enterica and Listeria monocytogenes. Chemical analysis identified 1-methoxyphenazine in the crude extracts of that strain as a likely contributor to the observed activity.9PubMed Central. Exploring the biosynthetic gene clusters in Brevibacterium: a comparative genomic analysis of diversity and distribution
For cheese safety, this matters because Listeria monocytogenes is one of the most dangerous foodborne pathogens associated with soft and surface-ripened cheeses. The moist, relatively neutral-pH rind of a washed cheese is an environment where Listeria can grow. If the resident Brevibacterium community produces compounds that suppress Listeria, the rind microbiome may serve as a natural protective barrier. This does not replace food safety protocols, but it does help explain why artisanal cheeses with well-established surface communities tend to be more resistant to pathogenic contamination than those made under sterile conditions with added commercial cultures. The ecological complexity of the rind works as a form of biological insurance.
B. Casei in Traditional and Non-Industrial Cheesemaking
B. casei does not only appear in European washed-rind cheeses. Researchers screening the microbial communities of animal skin bags used in traditional cheesemaking, a practice still found in parts of Central Asia and the Middle East, detected B. casei alongside lactic acid bacteria like Lactiplantibacillus plantarum and Streptococcus thermophilus.10Elsevier / International Journal of Food Microbiology. Microbial screening of animal skin bags used in traditional cheesemaking These skin bags are essentially natural bioreactors with their own embedded microbial flora, and B. casei’s presence in them suggests the organism has been a part of cheese cultures long before anyone deliberately selected it. Its role in these traditional systems is less well characterized than in European varieties, but the fact that it turns up in such different cheesemaking traditions speaks to how well-suited it is to the general conditions of milk fermentation and aging.
In industrial settings, B. casei is sometimes included in commercial ripening cultures sold to cheesemakers, though it is less commonly marketed by name than B. linens. Many commercial “B. linens” cultures, when subjected to modern genomic identification, turn out to contain B. casei or mixtures of Brevibacterium species. This taxonomic confusion has practical consequences: cheesemakers selecting cultures based on species labels may not be getting what they think they are, and the flavor outcomes can vary depending on which Brevibacterium species actually dominates the rind.
The Skin Connection and Body Odor
The resemblance between the smell of washed-rind cheese and the smell of unwashed feet is not a coincidence. Brevibacterium species, including B. casei, are part of the normal microbiota of human skin, especially in warm, moist areas like the feet and between the toes. On skin, they break down the amino acid methionine into methanethiol, the same volatile sulfur compound responsible for much of the “stinky cheese” aroma. The shared biochemistry means the same organism produces the same smell whether it is growing on a wheel of Munster or between your toes.11PubMed Central. Brevibacterium Species Infections in Humans—A Narrative Review
This dual habitat is part of what made the taxonomy so confusing before the 1980s formal classification. Strains from cheese and strains from skin looked similar under the microscope and behaved similarly in culture, but DNA analysis ultimately showed they were distinct enough to warrant separate species designations, with B. casei for the dairy strains and B. epidermidis for the skin strains. In practice, though, B. casei can be found on skin and B. epidermidis can show up in dairy, so the habitat boundaries are not absolute.
Opportunistic Infections in Immunocompromised Patients
Despite being considered harmless to healthy people, B. casei has been documented as a cause of bloodstream infections in immunocompromised patients. A case report described B. casei bacteremia and catheter-related sepsis in a patient with AIDS, with the organism isolated from a contaminated indwelling Hickmann catheter.12PubMed. Brevibacterium casei bacteremia and line sepsis in a patient with AIDS These infections are rare and almost always associated with central venous catheters or other medical devices that give the bacteria a direct route into the bloodstream. For the vast majority of people, eating cheese colonized by B. casei poses no health risk at all. The clinical concern is limited to hospital settings and severely immunocompromised individuals.
The organism’s ability to form biofilms on surfaces, a trait that serves it well when colonizing a cheese rind, unfortunately also allows it to adhere to catheter tubing and other implanted devices. This is a recurring theme in microbiology: the same traits that make a bacterium useful in food production can make it problematic in a clinical context. Recognizing B. casei as an emerging opportunistic pathogen is more about improving hospital infection control than about rethinking food safety.
Gluten-Degrading Enzymes and Potential Beyond Cheese
One of the more unexpected findings about B. casei comes from research into celiac disease. A strain designated B. casei NAB46, isolated from the human small intestine, was found to produce a prolyl endopeptidase capable of breaking down gluten proteins. The partially purified enzyme had a specific activity of 1.15 U/mg, and in laboratory tests it hydrolyzed immunotoxic gliadin peptides, the fragments of gluten that trigger the immune response in people with celiac disease.13Elsevier. Human small-intestinal gluten-degrading bacteria and its potential implication in celiac disease This is far from a treatment for celiac disease at this stage, but it illustrates how B. casei’s proteolytic toolkit, honed over millennia of protein-rich environments like cheese surfaces and the gut, could have applications outside of food science.
The enzyme’s ability to target proline-rich sequences is relevant because gluten proteins are unusually rich in proline and glutamine, which makes them resistant to the normal digestive enzymes in the human gut. Bacteria that have evolved specialized enzymes to cleave these bonds are of considerable interest to researchers looking for adjunct therapies that could reduce the amount of intact gluten reaching the small intestine. B. casei’s prolyl endopeptidase joins a growing list of microbial enzymes under investigation for this purpose, though none have yet made it into approved clinical use.
Why B. Casei Gets Overlooked
For decades, B. linens has been the Brevibacterium species synonymous with cheese ripening. Textbooks, cheesemaking manuals, and commercial culture catalogs all default to B. linens as the primary surface-ripening bacterium. B. casei’s relative obscurity is partly a historical accident. When the early microbiology of cheese was being worked out, culture-based methods could not easily distinguish between Brevibacterium species, and B. linens was described first and most thoroughly. Once it became the standard reference organism, researchers tended to identify cheese-surface isolates as B. linens unless there was a specific reason to look more closely.
Modern sequencing has changed this picture dramatically. Metagenomic and meta-transcriptomic studies consistently show B. casei as a dominant or co-dominant species on many cheese surfaces, sometimes outnumbering B. linens by a wide margin. The PLOS ONE study mentioned earlier, which found B. casei comprising 71% of bacterial reads at the end of ripening, is one example.5PLOS ONE. Overview of a Surface-Ripened Cheese Community Functioning by Meta-Omics Analyses Similar results have appeared across studies of different cheese types and geographic origins. The practical implication for cheesemakers is that understanding and managing B. casei specifically, rather than treating all Brevibacterium as interchangeable, could lead to more consistent and predictable flavor development.
Cheese science is still catching up to this realization. As more cheesemakers adopt molecular tools to monitor their ripening communities, B. casei’s contributions will likely become better defined and more deliberately harnessed. For now, it remains one of the most important organisms in surface-ripened cheese that most people have never heard of.