Streptococcus mutans is a facultatively anaerobic, gram-positive coccus (round bacterium) commonly found in the human oral cavity and is a significant contributor to tooth decay. It is part of the "streptococci" (plural, non-italic lowercase), an informal general name for all species in the genus Streptococcus. The microbe was first described by James Kilian Clarke in 1924. This bacterium, along with the closely related species Streptococcus sobrinus, can cohabit the mouth: Both contribute to oral disease, and the expense of differentiating them in laboratory testing is often not clinically necessary. Therefore, for clinical purposes they are often considered together as a group, called the mutans streptococci (plural, non-italic due to its being an informal group name). This grouping of similar bacteria with similar tropism can also be seen in the viridans streptococci, another group of Streptococcus species. Ecology S. mutans is naturally present in the human oral microbiota, along with at least 25 other species of oral streptococci. The taxonomy of these bacteria remains tentative. Different areas of the oral cavity present different ecological niches, and each species has specific properties for colonizing different oral sites. S. mutans is most prevalent on the pits and fissures, constituting 39% of the total streptococci in the oral cavity. Fewer S. mutans bacteria are found on the buccal surface (2–9%). Bacterial-fungal co-coaggregation can help to increase the cariogenic potential of S. mutans. A symbiotic relationship with S. mutans and Candida albicans leads to increased glucan production and increased biofilm formation. This therefore amplifies the cariogenic effect of S. mutans. Oral streptococci comprise both harmless and harmful bacteria. However, under special conditions commensal streptococci can become opportunistic pathogens, initiating disease and damaging the host. Imbalances in the microbial biota can initiate oral diseases. C. albicans is an opportunistic pathogenic yeast that can be found within the oral cavity. Its presence in the biofilm promotes higher levels of S. mutans when looking at early childhood caries. It stimulates the formation of S. mutans microcolonies. This is achieved through low concentrations of cross-kingdom metabolites, such as farnesol, derived from the biofilm. It has been suggested that when both microbes are present, more biofilm matrix is produced, with a greater density. When farnesol is in high concentration, it inhibits the growth of both S. mutans and C. albicans. This decreases the biofilm pathogenesis, and therefore its caries promoting potential. This offers the potential for an anti-fungal to be