Fusobacterium nucleatum is an oral bacterium, indigenous to the human oral cavity, that plays a role in periodontal disease. This organism is commonly recovered from different monomicrobial and mixed infections in humans and animals. It is a key component of periodontal plaque due to its abundance and its ability to coaggregate with other species in the oral cavity.
Research implicates periodontal disease caused by F. nucleatum with preterm births in humans. In many studies, F. nucleatum cells have been isolated from the amniotic fluid, placenta, and chorioamnionic membranes of women delivering prematurely. Moreover, laboratory rats inoculated with F. nucleatum have been found to deliver prematurely, and the pathology of the infection seems to mirror observations in humans. Together, this research provides strong evidence for a causal connection between F. nucleatum-caused periodontal disease and at least some cases of preterm delivery.
F. nucleatum has a demonstrated association with colon cancer; in addition, a mechanism has been described by which F. nucleatum induces tumor growth without the more general mechanism of inducing inflammation or otherwise irritating the colon tissue. This suggests direct and specific carcinogenesis. 
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