Postbiotic

Postbiotic

Postbiotics are preparations of inanimate microorganisms and/or their components that confer a health benefit on the host. In 2021, the International Scientific Association for Probiotics and Prebiotics (ISAPP) issued a consensus definition that helped align terminology across research and applications ^[1]. This article summarizes key concepts, an industry-oriented classification proposed by the International Probiotics Association (IPA), preparation methods and components, proposed mechanisms, current evidence in clinical and preclinical settings, and safety and regulatory considerations.

Definition

A postbiotic is a "preparation of inanimate microorganisms and/or their components that confers a health benefit on the host" ^[1]. Under this consensus, postbiotics include inactivated microbial cells or cell components, with or without co-present metabolites, but exclude substantially purified metabolites alone, vaccines, filtrates devoid of cell components, and purely synthetic compounds ^[1]. The microbial source should be defined, and the inactivation process and matrix characterized ^[1].

Terminology

Before the ISAPP consensus, related terms such as paraprobiotics (inactivated or non-viable microbial cells or their crude extracts), ghost probiotics, and tyndallized probiotics were used in the literature ^[2][3]. When the ISAPP criteria are met, postbiotic is recommended as the unifying term; paraprobiotics can be considered a subset emphasizing cellular components ^[1][2][3].

Classification (industry-oriented; IPA framework)

The International Probiotics Association (IPA) proposed an industry-oriented decision tree and four subcategories for non-viable microbial ingredients used in foods/dietary supplements: CX (complex non-viable microbial preparations)—unpurified culture medium containing intentionally inactivated cells and/or cell fractions; IC (intact non-viable microbial cells)—intentionally inactivated whole cells separated from the culture medium; FC (fragmented microbial cells)—intentionally fragmented cells (e.g., lysates/extracts) separated from the culture medium; and MM (microbial metabolic products)—metabolic products in unpurified or partially purified culture medium. Nature-identical synthetic components and single purified molecules are excluded; microbial origin is required. This framework aims to harmonize nomenclature, standardization and labeling in commercial contexts, and its scope may not fully align with all academic definitions ^[4].

Preparation and Components

Postbiotics are obtained by deliberate inactivation of well-characterized microorganisms. In manufacturing for foods and supplements, physical inactivation methods are preferred to ensure safety and avoid chemical residues. Common approaches include thermal processing (e.g., pasteurization, tyndallization) and non-thermal methods such as high-pressure processing, irradiation, and sonication ^[1][5]. Preparations may contain cell wall fragments (e.g., peptidoglycan, teichoic acids), surface proteins (e.g., S-layer proteins, pili), exopolysaccharides, and metabolites present in the matrix. Transparent reporting of the starting strain(s), inactivation method, and matrix is recommended ^[1][6].

Proposed Mechanisms

Proposed mechanisms include modulation of mucosal immune responses via microbe-associated molecular patterns interacting with host pattern-recognition receptors; support of epithelial barrier function (e.g., tight-junction signaling); antagonism against microbes via bacteriocins or organic acids; and systemic signaling influencing metabolic pathways ^[1]. In vitro findings with a mixed postbiotic preparation have reported anti-inflammatory and antioxidant effects, increased expression of epithelial tight-junction genes, and promotion of beneficial bacteria ^[7].

Evidence and applications

Clinical evidence

Evidence is emerging across pediatric and adult populations, with reviews summarizing potential roles in gastrointestinal health (e.g., symptom management in functional bowel disorders), immune support (e.g., reducing common infections), and other areas ^[6][8]. Small randomized trials in oral health have reported increased salivary IgA and improvements in oral hygiene outcomes with heat-killed strains or postbiotic lozenges ^[9][10].

Preclinical evidence

In mouse models of loperamide-induced constipation, multi-strain probiotic formulations with a defined postbiotic added relieved constipation-related endpoints and were associated with shifts in gut microbiota composition, gastrointestinal regulatory transmitters, inflammatory cytokines, and fecal short-chain fatty acids ^[11]. Separately, in vitro work with a mixed postbiotic preparation supports anti-inflammatory, antioxidant, and barrier-supporting activities, along with growth promotion of beneficial bacteria ^[7][. These findings warrant confirmation in well-designed human studies.

Safety and Regulation

Because postbiotics are non-viable, they avoid risks related to microbial translocation or infection inherent to live microbes; nonetheless, safety should be evaluated case-by-case (e.g., endotoxin levels, processing residuals, immunological responses) [1]. Postbiotics are not a distinct regulatory category; products are typically evaluated under existing frameworks (e.g., foods, dietary ingredients, or medicines) [1, 4].

Commonly used taxa

Many postbiotic preparations derive from taxa also used as probiotics, notably Bifidobacterium and lactobacilli (including Lactobacillus sensu lato and reclassified genera), as well as Lactococcus and Streptococcus. Evidence and safety are strain-specific and require individual evaluation [6, 8].