Spirillum in microbiology refers to a bacterium with a cell body that twists like a spiral. It is the third distinct bacterial cell shape type besides coccus and bacillus cells. Spirillum is a genus of Gram-negative bacteria (family Spirillaceae). There are two species, Spirillum volutans and Spirillum winogradskyi. The taxonomic position of Spirillum minus and Spirillum pulli is uncertain. Spirillum minus is associated with rat-bite fever.It is a genus comprising elongated forms having tufts of flagellae at both poles and usually living in stagnant water rich in organic matter. They are twisted and aerobic.