Overview: Bacteria of genus Leptotrichia are abundant in the healthy mouth, making up 3% or more of the bacteria in dental plaque and on the tongue, tonsils, and throat. Many of the species recognized in HOMD are as yet unnamed. The unnamed taxa L. sp. HMT 215 is abundant on the tongue dorsum whereas L. buccalis, L. hongkongensis, and the unnamed L. spp. HMT 212 and 392 are abundant in dental plaque. Some species, including HMT 221 which is abundant on the tongue dorsum, were reclassified into the genus Pseudoleptotrichia in 2020 (Eisenberg et al. 2020).

Ecological role/importance in health and disease: Leptotrichia spp. are anaerobic or microaerophilic. In the "hedgehog" structure of dental plaque, together with Fusobacterium spp. they occupy a presumably anoxic zone in the interior of the structure (Mark Welch et al. 2016). Leptotrichia spp. may also cause opportunistic infections.