Casei

Casei is most commonly encountered as the specific epithet in the name Lactobacillus casei, a lactic acid bacterium widely used in dairy fermentation. Members of this species are Gram-positive, non-spore-forming, and ferment carbohydrates to lactic acid. They occur naturally in milk, fermented dairy products, and the human gastrointestinal tract, where they contribute to acidification, flavor development, and, in some cases, competitive exclusion of spoilage organisms.

Taxonomy and naming of this organism have been subject to revision. In modern databases, many strains historically labeled as Lactobacillus casei are now placed in the related genus Lacticaseibacillus, and the species name may appear as Lacticaseibacillus casei in current classifications. Related species in the broader casei/paracasei group are commonly grouped together due to similarities in physiology and genetics, and some references continue to use traditional nomenclature.

Industrial and probiotic roles are notable. L. casei strains are used as starter cultures in cheese, yogurt, and other fermented dairy products, where they contribute to acid production, texture, and flavor. Some strains have been developed as probiotics and studied for potential benefits to gut health, immune function, and symptom relief in certain conditions; however, effects are highly strain-specific and not universal. A well-known probiotic example is a Shirota-type strain used in commercial products, illustrating the diversity of applications within the species.

Safety and regulation are generally favorable for food- and probiotic-grade strains. Lactobacillus casei strains are commonly regarded as safe when used as intended, but regulatory approvals and monitoring apply to health claims and specific probiotic formulations. In immunocompromised individuals, rare infections have been reported, underscoring the importance of strain-specific risk assessment.