Comparison of the morphology, antigenicity, and pathology of Nichols and Birmingham isolates of Treponema pallidum.

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Abstract
A strain of T. pallidum isolated from a homosexually acquired penile chancre in Birmingham [England, UK] in 1979 was serially passaged in rabbits and compared with the Nichols strain. The 2 strains appeared identical morphologically; no gross differences were detected on antigenic analysis by 2-dimensional immunoelectrophoresis. The Birmingham strain was considerably less virulent for rabbits; the number of organisms required for equivalent time of development severity of skin lesions was 10-fold greater for the Birmingham strain. The pathology of testicular infection was broadly similar for both strains.