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The purified membranes of Serpulina hyodysenteriae was examined to determine whether they contained cholesterol. The study made use of discontinuous sucrose density gradients to isolate outer and inner membranes. Results revealed that the outer and inner membrane fractions contained less than 1% and 2% of the total NADH oxidase activity in the cell lysate. Treatment with different concentrations of digitonin showed that the outer membrane could be selectively be removed at concentrations to about 0.125%.

Isopycnic centrifugation using sucrose density gradations isolates the inner and outer membranes of Borrelia burgdorferi and assists in its characterization. A soluble marker and an inner membrane marker help in the structural and component analysis of the outer membrane, which contains small quantities of flagellin protein, implying that it is almost pure. The number of intramembranous particles per square micrometer in the outer and inner membrane is 6,600 and 1,700 respectively, as revealed by freeze-fracture electron microscopy.