spirillum n spirally twisted elongate rodlike bacteria usually living in stagnant water n any flagellated aerobic bacteria having a spirally twisted rodlike form Usage(s) One is a wriggly spirillum, the other a cigar-shaped bacillus. That is a spirillum that lives in the blood of rats and mice. Both the fusiform bacillus and Vincent's spirillum (perhaps they are the same) are anaerobic (cannot live in oxygen). Synonym(s) spirilla