Bifidobacterium longum subsp. longum ATCC 55813

*Bifidobacterium longum subsp. longum ATCC 55813* is a gram-positive, rod-shaped bacterium best categorized as a heterotroph. This species thrives optimally at a temperature range of 30–37°C and is classified as an obligate anaerobe, meaning it requires an oxygen-free environment to grow and reproduce. Bifidobacterium longum subsp. longum is commonly found in the gastrointestinal tracts of various mammals, including humans, where it participates significantly in maintaining gut health. It colonizes various body sites, particularly the colon, but can also be present in the oral cavity and the vaginal microbiota. As a member of the Bifidobacteriaceae family, *B. longum* plays a critical role in the microbiome by contributing to the fermentation of dietary fibers, producing beneficial short-chain fatty acids like acetate and lactate. These byproducts help regulate gut pH and serve as energy sources for colonic cells. The presence of *B. longum* is associated with numerous health benefits, including enhanced immune function, improved digestion, and protection against intestinal pathogens. Research indicates that *B. longum* may also exert anti-inflammatory effects, making it a focus of interest in studies related to conditions such as irritable bowel syndrome (IBS) and inflammatory bowel diseases (IBD). Moreover, this strain has been utilized in probiotic formulations aimed at restoring microbial balance in individuals whose gut microbiota has been disrupted by antibiotic usage or gastrointestinal infections. Its robust nature and ability to adapt to various environments reinforce its potential as a therapeutic agent in promoting gut health and overall wellness.