Spirochaetes: past lessons to future directions [Editorial]

Spirochaetes today are often sidelined as an interesting exception within the microbial world, yet spirochaetes have played a major role in our understanding of microbial pathogenesis. As a group, they have challenged our established understanding of microbial infections, and still have a plethora of other secrets to disclose. Within this themed issue, we examine a range of spirochaetal examples, ranging from relapsing fever, the expanding group of Borrelia burgdorferi sensu lato, through to Leptospira and the complex polymicrobial role of oral treponemes in causing periodontitis. Each of these examples provides challenges to our accepted views and thus serves to stimulate new concepts, adding to our understanding of the mechanisms of pathogenesis.