Characteristic morphology of Borrelia burgdorferi seen by various techniques following one week of culture in BSKII medium. A and B: Dark field microscopy images of Borrelia burgdorferi strain B31 showing the usual spiral form of spirochetes (A) and their agglomeration into colony-like masses (B). Similar spiral morphology of strain B31 is illustrated by OspA immunoreactivity (C) and by atomic force microscopy (AFM) imaging (D). E and F: Dark field microscopy images showing the typical spiral form (E) and colony formation (F) of Borrelia burgdorferi strain ADB1. G: Similar spiral morphology of strain ADB1 shown by immunostaining with a polyclonal anti-Borrelia burgdorferi antibody (Biodesign, B65302R). The green fluorescent immunoreaction was revealed with an FITC tagged secondary antibody. H: Similar morphology of strain ADB1 revealed by silver impregnation with the Bosma Steiner microwave technique. Bars: A, C = 10 μm; B = 30 μm; D = 1 μm; E, G, H = 8 μm; F = 25 μm.