Because the participants could very easily spread it to other people. This wouldn’t just affect them. That’s why the trial was ultimately required to take place under quarantine.
It’s not even a question of whether it would spread, but whether it might spread. There’s a reasonable chance that this bacterium would, in fact, spread, and nobody has proven otherwise.
The FDA is doing its job here: it’s protecting the masses from people who believe they’re just consenting for themselves.
The FDA, however, is not regulating the spread of the 800 other known species of oral bacteria as well as presumably numerous unknown ones, which do cause some known harm. The extreme suspicion of commercially introduced anthropogenic agents seems a bit ridiculous in both natural ecology and the human microbiome. Prove this compound conclusively safe, but not these other ten million compounds we're just going to allow to run wild. Or for competitors - rely on the 'proof' of safety established in the 1920's or the 1970's before we had any idea whatsoever what we were doing scientifically. Or just rely on doctors/dentists unsupported first-principles advice - we've never demonstrated scientifically that floss works, for example.
We should all be quarantined, all the time, by this criteria. Regulatory bodies have a great cognitive bias towards fictional 'purity' of systems that are in actual scientific fact, messy and routinely contaminated in various ways.
For testing, we do what we can within practical limits. What those limits should be, is where contention lies. The FDA will come around, especially if someone else does trials under less strict conditions. Won't happen today.
All of those other oral probiotics are based on published research about naturally occurring bacterial strains already present in the environment, and in some cases have the evidentiary support of human trials.
Lumina is a genetically modified bacteria. It has no research supporting its effectiveness because the original inventors never bothered to conduct a human trial; they just said that it probably works based on testing in a petri dish. (Note: lots of drugs work in petri dishes and laboratory animals. Very few go on to have success in humans.)
Notably, the founder of the current company selling it has does not have a background in dentistry or microbiology and does not understand how his company's product actually works.
> research supporting its effectiveness because the original inventors never bothered to conduct a human trial; they just
If you had read the article you would know that they did bother but the regulatory body set requirements for such a study so high that they couldn't perform it.
> The extreme suspicion of commercially introduced anthropogenic agents seems a bit ridiculous in both natural ecology and the human microbiome. Prove this compound conclusively safe, but not these other ten million compounds we're just going to allow to run wild.
With endemic organisms (or viruses) they just are going to run wild regardless of how we feel about it. There's no point in banning a naturally occurring algae because excluding it from the environment is not a practical option.
The only time when we have any strong control over what organisms are in an environment is when they don't yet exist there, but we have the ability to introduce them. This is our only technical choke-point, so it makes a lot of sense to make a big deal of that decision, and probably to be quite conservative about it. You can always let the cat out of the bag later, but you can never get it back in.
It’s not even a question of whether it would spread, but whether it might spread. There’s a reasonable chance that this bacterium would, in fact, spread, and nobody has proven otherwise.
The FDA is doing its job here: it’s protecting the masses from people who believe they’re just consenting for themselves.