Microbial Reservoirs in Artisanal Dairy Products from Spain and Algeria Harbor Lactic Acid Bacteria with Significant Gluten-Degrading Activity

Celiac disease (CD) is an autoimmune disorder triggered by immunogenic gluten peptides that resist gastrointestinal digestion. The only current treatment is a strict gluten-free diet, which is challenging to maintain. Lactic acid bacteria (LAB) with specific proteolytic systems offer a promising strategy for gluten detoxification. This study aims to isolate and characterize gluten-degrading LAB from traditional Spanish and Algerian dairy products. A total of 27 artisanal dairy samples were collected. LAB were isolated on MRS and Elliker agar. Gluten-degrading activity was screened using a well diffusion assay with cell-free supernatants and a spot assay with live cultures. Active isolates were identified by 16S rRNA gene sequencing. Out of 123 isolates, 40 (32.5%) were positive in the well assay, while 67 (54.5%) were positive in the spot assay, indicating the latter's higher sensitivity for detecting cell-associated proteases. Halo diameters ranged from 6 to 16 mm. Algerian isolates exhibited significantly stronger activity (mean halo: 12.6 ± 2.1 mm) compared to Spanish isolates (10.2 ± 2.0 mm; p < 0.001). Molecular identification of the 32 most active isolates revealed dominant species as Lactiplantibacillus plantarum, L. pentosus, Levilactobacillus brevis, and Enterococcus faecium. This study confirms that artisanal dairy fermentations are rich sources of LAB with robust gluten-degrading potential. The superior activity of Lactiplantibacillus spp. aligns with their complex peptidase systems. The geographical variation highlights the influence of local fermentation practices. Selected strains represent excellent candidates for developing adjunct cultures to produce gluten-reduced foods and novel probiotic therapeutics.