Germ,microbe,bacterium,bacillus,virus:

　　Thoughnotstrictsynonyms,arecomparablebecausealldenoteorganismsinvisibletothenakedeye,includingorganismsthatarethecausativeagentsofvariousdiseases.

　　Germandmicrobearetheordinarynonscientificnamesforsuchanorganismandespeciallyforonethatcausesdisease.

　　Bacteria,thepluralofbacteriumandtheformcommonlyingeneraluse,isoftenemployedastheequivalentofdesignationofalargegroupofprokaryoticmicrobeswhicharefoundwidelydistributedinwater,air,soil,livingthings,anddeadorganicmatter,whichhavestructuralandbiologicalcharacteristicsdistinguishingthemfromotherunicellularmicroorganisms(asprotozoans),andonlysomeofwhichareinstrumentalinproducingdiseaseinman,animals,andplants.Inadditiontothepathogenicordisease-causingbacteriatherearethesaprophyticbacteriawhichliveupondeadordecayingorganicmatterandwhich,forthemostpart,arebeneficialintheireffectswhichincludemanynaturalchemicalprocesses(asfermentation,oxidation,andnitrification).

　　FromMerriam-Webster’sDictionaryofsynonyms