Internal cores of M. pneumoniae observed by negative-staining EM.

(A) Untreated cell bound to a carbon-coated grid. The membrane protrusion at the right pole is the attachment organelle. (B) Cell treated with 1% Tween 20. The cell was treated on a grid. The cell membrane was partially damaged, and the internal core remained at the right pole of the cell. (C) Magnified image of (B). (D) Core fraction isolated through sucrose-gradient centrifugation after cells were treated by 1% extraction of Triton X-100. (E) The boxed area of (D) is magnified. The same magnification was applied to (A), (B), and (E).