Atypical cystic spirochetes in the medium of neuronal and astrocytic cultures following 1 week exposure to Borrelia burgdorferi . A-C and H are dark field microscopy images. Panels D-G illustrate immunostaining with anti-OspA antibody. A: In addition to typical spiral-shaped spirochetes, several rolled, looped, and ring-shaped forms are seen. B: Atypical spirochetes showing ring shaped forms, blebs still attached to the spirochetes (arrows) as well as some minute granules. C: Arrow points to a bleb still attached to the surface of the spirochete. Multiple ring-shaped (D, E) and cystic forms (F, G) are visible. Notice that in G the cyst is formed by two spirochetes. H-J: Borrelia cysts as visualized by dark field microscopy; the arrow points to the end of the spirochete forming the cyst. Cyst form as seen by immunofluorescence using anti-OspA antibody (I) and DAPI-DNA staining (J). K: OspA immunoreactive thick, elongated bodies were also observed. Panels A-G correspond to strain ADB1 and H-K to strain B31. Bars: A, B = 10 μm; C = 4 μm; D = 8 μm; E, F = 6 μm; G = 5 μm; H-K = 4 μm.