The nimble helices are spirochetes, extraordinarily mobile, flexing and creeping over solid surfaces. They too are rare in captivity, but they're worth keeping an eye on, since they're implicated in periodontal disease. Buffy becomes excited, spotting Trichmonas, a huge ponderous thing with a topknot of flagella. While Buffy is passing out handouts about fungi, I will slip over and give it a kiss. I take a superior attitude to Buffy's warnings about fungi, since I want to be sure everyone on the tour knows that I know all this already.
Bacteria seem to keep fungi at bay, notably various species of Candida.
The best known, Candida albicans, a cream colored fungus that likes your tongue, is found in small number in 45 percent of adults. In babies and in immunocompromised people it sometimes flourishes under the old-fashioned name thrush. Adults with sturdy immune systems sometimes get thrush after prolonged use of antibiotics, which kill off the bacteria and let the fungus run amok. Buffy has spoken optimistically of recent sightings. They are apparently scavengers, so while they're often seen in cases of periodontal disease, they don't cause it, any more than a vulture kills its own dinner.