This documentary is about microorganisms that live, compete, feed, and breed on the surface or in the depths of our bodies.
| Actor | Role |
|---|---|
 Marta DusseldorpNarrator (voice) | Narrator (voice) |
| GGarin AgliettiHimself | Himself |
| KKati AngelidisHerself | Herself |
| TThomas BorodyHimself | Himself |
| MMaya ColemanDaughter | Daughter |
| AAlan CooperHimself | Himself |
| JJohn CroeseHimself | Himself |
| RRob DunnHimself | Himself |
| RRichard FaulksHimself | Himself |
| AAndrew FergusonHimself | Himself |
| JJaroslav FlegrHimself | Himself |
| NNeville GullyHimself | Himself |
| JJon HangerHimself | Himself |
| PPhil HugenholtzHimself | Himself |
| JJohn KaidonisHimself | Himself |
| AAden KlauserBaby | Baby |
| WWilliam KostopoulosHimself | Himself |
 Sharon LewinHerself | Herself |
| JJorge A. LlamasHimself | Himself |
| AAlex LoukasHimself | Himself |
| CChristopher LowryHimself | Himself |
| BBrian MalowHimself | Himself |
| BBarry MarshallHimself | Himself |
| NNatalie McCurryMum | Mum |
| HHolly MenningerHerself | Herself |
 Milan NashtSon | Son |
| SScott O'NeillHimself | Himself |
| JJonice PadilhaHerself | Herself |
| DDavid PatersonHimself | Himself |
| BBruce PauleyHimself | Himself |