Hiding in Plain Sight: Colonic Spirochetosis in Humans

In 1967, Harland and Lee made a startling discovery: in some humans, the colonic epithelium is covered with a forest of spirochetes (W. A. Harlan, and F. D. Lee, Br Med J 3:718-719, 1967, https://doi.org/10.1136/bmj.3.5567.718). In this issue of Journal of Bacteriology, Thorell et al. present a systematic analysis of the prevalence and diversity of the spirochetes Brachyspira aalborgi and Brachyspira pilosicoli in the human colon. These and prior studies provide avenues toward resolving important questions: what bacterial and host parameters contribute to this extensive colonization, and what impact does it have on human health?