Methods for preventing, treating or diagnosing Type 1 Diabetes (T1D) are described. Amyloid-producing bacteria within microbiota are inactivated. Amyloid-producing bacteria are inactivated in microbiota, gastrointestinal tract, bodily fluids or tissues. Type-1 Diabetes associated microbial product production or release by microbiota is prevented. Also described is inactivation of bacteria-derived T1DAMP present in microbiota, bodily fluids or tissues of a mammal. Release of bacteria-derived T1DAMP from biofilm or bacteria to gastrointestinal tract is inhibited. Entry of bacteria-derived T1DAMP to microbiota, gastrointestinal tract, bodily fluids or tissues of a mammal is inhibited.