Coiling phagocytosis is the predominant mechanism for uptake of the colonic spirochetosis bacterium Serpulina pilosicoli by human monocytes

Serpulina pilosicoli is a newly identified pathogenic spirochete that estab lishes persistent colonic infections in human beings and animals. Macrophag es are one of the key defenses against invasion of mucosal surfaces by bact erial pathogens. Macrophages engulf many bacteria by conventional phagocyto sis; however recent studies indicate coiling phagocytosis as a new and impo rtant mechanism for internalization of Legionella pneumophila and spirochet es of the genus Borrelia, Leptospira, and Treponema. In this study, THP-1 h uman monocytic cells were incubated with the human S. pilosicoli strain SP1 6 and the contribution of coiling and conventional phagocytosis to the tota l number of phagocytic events were determined by sequential ultrastructural examination between 5 and 45 minutes. The frequency of phagocytosis increa sed over time from 5.1% after 5 minutes up to 21.9% after 45 minutes with g reater than 70% of the events involving coiling phagocytosis. The data indi cate that coiling phagocytosis may be a universal mechanism for uptake of p athogenic spirochetes.