Significance of Asaccharolytic Eubacterium and Closely Related Bacterial Species in the Human Oral Cavity

Asaccharolytic Eubacterium species are obligate anaerobic, gram-positive rods frequently isolated from human oral specimens, particularly from infectious lesions, such as periodontal pockets and apical lesions. Many unknown bacterial strains have recently been isolated from infectious lesions. These strains were determined to be mainly asaccharolytic Eubacterium and/or phylogenetically closely related species. Many novel genera, such as Slackia, Eggerthella, Cryptobacterium, and Mogibacterium, have been established by molecular systematic techniques, including 16S rRNA gene sequencing analysis and DNA–DNA hybridization. Moreover, many species within the genus Eubacterium have been reclassified based on phylogenetic data. Many uncultured, undescribed, and unknown bacterial species thrive in the human oral cavity. However, to elucidate the etiology of oral infections and to develop novel diagnostic tools, a complete description of the microbial flora associated with these infections is required. This review focuses on recent findings on asaccharolytic Eubacterium and closely related bacterial species in the human oral cavity and on the etiological role of these bacterial species in oral infections in humans.