The morphology and ultrastructure of two strains of Borrelia anserina
were investigated by electron microscopy of negatively stained and ult
rathin sectioned cells. One was a cultivable strain originally isolate
d in the USA and the other was originally isolated in Nigeria and main
tained in chickens. The cells were regularly helical, 9-21 mu m long a
nd 0.22-0.26 mu m wide with a helix wavelength of about 1.7 mu m. The
cells were surrounded by a surface layer and appeared to divide by bin
ary fission. The structure of the cells from each of the two strains w
as identical except that those of the USA strain possessed seven flage
lla inserted at each end and those from the Nigerian strain had eight.