Coming back to this post I actually think it is also not ok to put otters and orangutans in the same enclosure. I think this zoo took a pretty big risk but it happened to turn out ok. The orangutans might just as well have thrown the otters against the enclosure walls on their first encounter.Ok so orangutans and otters in the same enclosure is fine but let's say swordtails and platies arent ? I get not mixing dart frogs, or any other delicate vivarium animals. I think most of us on here are not dumb enough ( I hope ) to mix different species requiring different environmental parameters, size differences, predator/prey relationships etc. Same goes with fish, fresh or salt. I'm not going stick a Cynotilapia afra in with a school of cardinal tetras in a blackwater tank. But I see no problem with a blackwater biotope tank consisting of the aforementioned cardinal tetras, some discrossus cichlids, apistogrammas, etc.
Mixing species in an enclosure, whether it be frogs or tropical fish is most likely (note: here I am using "likely" as a vernacular statement relating to probability) to wipe out your charges, and far less likely to create a global pandemic in novel lineages. Not impossible of course.
Fungi do not work the same way as viruses (who can easily incorporate new genetic material into their own) but there is still al lot of potential for exchanging genetic material between strains/species.