Pleomorphic forms of B. burgdorferi are not CWD. (a) TEM micrographs of Epon-embedded spirochaetes, blebs, 2 h H2O RBs, 4 days HS RBs and cells with outer membrane damage induced by treatment with 100 µg doxycycline ml−1 for 24 h. Blebs were prepared by induction of 2 h H2O RBs and were then reintroduced to normal culture medium and incubated for 1 h at 37 °C. The upper panels represent the overall view of the whole cell, and expanded insets in the lower panels indicate the zoomed morphology of the outer envelope. The outer membrane (om), inner membrane (im) and protoplasmic cylinder (pc) are easily discernible in zoomed images. The lower panel of the doxycycline-treated spirochaete illustrates the damaged outer membrane (dom). (b) TEM images of swollen 4 days HS RB with swollen protoplasmic cylinder. Left panel illustrates the RB with normal size protoplasmic cylinders (pc) and one swollen protoplasmic cylinder (spc). Right panel displays the zoomed view of the swollen protoplasmic cylinder.