fusobacterium nucleatum fusobacterium nucleatum fusobacterium nucleatum is a gram-negative, anaerobic oral bacterium, commensal to the human oral cavity, that plays a role in periodontal disease. this organism is commonly recovered from different monocultured microbial and mixed infections in humans and animals. in health and disease, it is a key component of periodontal plaque due to its abundance and its ability to coaggregate with other bacteria species in the oral cavity.