This is a type of gram-negative, anaerobic bacterium that does not produce spores. It can be found in the normal oral, upper respiratory, genital, and gastrointestinal areas of the body, and it is associated with infections in the mouth, lungs, and brain. In cases of acute necrotizing gingivitis, it is frequently found alongside spirochetes, specifically Treponema vincentii. This bacterium is sometimes referred to as Bacillus fusiformis.