A spirochete bacterium responsible for syphilis.
The infective agent of syphilis, slender spiral filament around 10 pm in length with 6-12 sharp, regular corkscrew coils. Demonstrated by dark-ground microscopy, silver impregnation (e.g., Fontana, Levaditi) methods or by fluorescent antibody techniques. Cultivable with difficulty under anaerobic conditions in, for example, Noguchi’s medium. Apart from demonstration of the spirochaete in primary lesions, syphilis is diagnosed by a number of immunological tests, which with allied topics are listed under syphilis.