Other Borrelia Species and Spirillum minus

Microbiology

Members of the genus Borrelia are microaerophilic spirochetal bacteria characterized morphologically by coarse and irregularly shaped coils, with a cell wall and an inner cytoplasmic membrane between which are multiple flagella that provide corkscrew-like motility. Substantially thicker than the Treponema spp., Borrelia spp. stain easily with aniline or acid dyes and can be visualized on light microscopy in Wright- or Giemsa-stained blood smears. Isolation of the organism is difficult, requiring special media, and growth is slow.

Few Borrelia spp. are recognized human pathogens. By changing the antigenic structure of their surface proteins, they can temporarily elude host defenses, thus resulting in “relapsing fever” in infected humans. The resolution of symptomatic stages of the illness correlates with peak concentrations of antibodies against specific antigens. Borreliae cause vasculitis, with a predilection for capillaries and small arterioles of any organ, especially the reticuloendothelial system, bone marrow, and central nervous system.