Rolled and cystic forms of Borrelia burgdoferi spirochetes observed after one week of culture in medium to which Thioflavin S had been added. A: Observation by Thioflavin S fluorescence. Arrows point to rolled cystic forms at the periphery of an agglomerated mass of spirochetes from strain B31. Rolled (B) and cystic (C) forms observed by dark field microscopy (strain B31). D and E: Cyst forms of Borrelia burgdorferi (strains ADB1 and B31, respectively) following immunostaining with the monoclonal anti-OspA antibody. F-H: Atomic force microscopy (AFM) images of Borrelia cysts. Rolled spirochetes are clearly visible in F (strain B31) and G (strain ADB1). Arrow in G shows that the cyst is formed by two spirochetes rolled together. H: The cystic form is entirely covered by a thickened external membrane masking the content of the cyst (strain B31). Bars: A-D = 6 μm; E = 5 μm; F = 1 μm; G = 2.5 μm; H = 0.5 μm.