WordNet (r) 3.0 (2006):

spirochete
    n 1: parasitic or free-living bacteria; many pathogenic to
         humans and other animals [syn: spirochete, spirochaete]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "spirochete":
   adenovirus, aerobe, aerobic bacteria, amoeba, anaerobe,
   anaerobic bacteria, bacillus, bacteria, bacterium, bug, coccus,
   disease-producing microorganism, echovirus, enterovirus,
   filterable virus, fungus, germ, gram-negative bacteria,
   gram-positive bacteria, microbe, microorganism, mold,
   nonfilterable virus, pathogen, picornavirus, protozoa, protozoon,
   reovirus, rhinovirus, rickettsia, spirillum, spore, staphylococcus,
   streptococcus, trypanosome, vibrio, virus