Bacillus Clausii is a rod-shaped, gramme-positive, sporing bacterium, which is naturally resistant to most common antibiotics and also very resilient to the acidic conditions of the human stomach. It has a distinct endospore form and unlike most of the classic lactic-acid-based probiotics, the endospore structure serves as a protective shell, enabling it to pass through the gastrointestinal tract intact in large quantities and reach the intestines without dying.