Gastric microbiota‑derived postbiotics as antimicrobial and anti‑biofilm agents

The human gastric microbiota is recognized as a diverse and metabolically active ecosystem with significant roles in health and disease. Beyond probiotics, postbiotics, non-viable microbial products with antimicrobial and anti-biofilm properties, offer stable and safer therapeutic alternatives. Rising antimicrobial resistance and biofilm associated infections caused by pathogens such as Staphylococcus aureus and Candida albicans highlight the urgent need for new strategies. Based on this evidence, the present study aimed to isolate bacterial strains from gastric biopsies of patients with gastritis, evaluate their probiotic traits with molecular confirmation, and prepare postbiotics from these strains. The antimicrobial and anti-biofilm activities of the postbiotics were then tested in vitro against S. aureus and C. albicans , two clinically relevant biofilm-forming pathogens. From 20 gastric biopsies, 65 isolates were recovered, mostly Gram‑positive bacilli ( n = 52). β‑hemolytic strains ( n = 29) were excluded, leaving 34 for probiotic screening. Nine isolates survived strongly at pH 2.5 (> 10⁶ CFU/mL), and several showed bile salt resistances with inhibition rates between 0.1 ± 0.1 and 2.4 ± 0.3. 2 isolates maintained high viable counts under simulated gastric juice at 4 h and 24 h, adhered strongly to Caco‑2 cells, and produced ammonia from L‑arginine. 16S rRNA sequencing identified one (Q3) as Lacticaseibacillus and the other (M2) as Ligilactobacillus. Both were resistant to vancomycin, ceftazidime, and amikacin. Postbiotics were prepared from extracellular and intracellular metabolites through centrifugation, filtration, lysis, and lyophilization, yielding PQ3 and PM2. MIC assays showed PQ3 inhibited S. aureus at 0.125 g/mL and C. albicans at 0.5 g/mL, while PM2 was more potent (0.0625 g/mL and 0.125 g/mL, p < 0.0001). MBC/MFC assays confirmed stronger killing by PM2, with bactericidal activity at 0.125 g/mL versus 0.25 g/mL for PQ3, and fungicidal activity at 0.5 g/mL versus 1.0 g/mL ( p < 0.0001). Biofilm assays revealed PQ3 reduced S. aureus biofilms by 18–49% and C. albicans by 28–51%, whereas PM2 achieved 27–74% and 56–85% inhibition respectively ( p < 0.0001). Gastric‑derived postbiotics demonstrated strong antibacterial, antifungal, and anti‑biofilm activity. These results highlight their promise for future investigation, although in vivo validation, future genomic and mechanistic studies are needed to further support the therapeutic potentials of gastric‑derived postbiotics.