IgE-Binding Bacterial Components Not Yet Documented in the Allergen Databases and Their Allergenic Mechanisms: An EAACI Position Paper.

Among bacteria that are associated with the development and/or exacerbation of allergic/atopic diseases, several have been described to produce IgE-binding components. However, only one bacterial protein, Bac s 1, is currently listed in the official database of the World Health Organization/International Union of Immunological Societies (WHO/IUIS) Allergen Nomenclature Sub-Committee. The aim of this position paper was to identify potential bacterial allergens and their reported clinical relevance in the published literature and consider candidates for the Allergen Nomenclature database. PubMed and the WHO/IUIS Allergen Nomenclature database were searched up to October 2025. Consensus was obtained during task force meetings and by a written commentary process. Sixty-six IgE-binding components in 20 different species of bacteria were found, most associated with clinical symptoms. Allergen candidates include staphylococcal superantigens, bacterial enzymes, and components from two Chlamydia species, some of which are potential marker allergens for disease severity. The results point to long-neglected evidence of "bacterial allergy" that in certain cases may be induced by unconventional mechanisms. Diseases that are currently considered non-allergic might be re-classified as allergic if these IgE-binding components are recognized as allergens and used for diagnosis in the future.