July 01, 2013

The brain microbiome: extraordinary claims require extraordinary evidence

The podcast This week in Microbiology (aka TWiM; http://www.microbeworld.org/podcasts/this-week-in-microbiology/archives/1418-twim-58-the-brain-microbiome) has this week featured discussion on the Brain Microbiome on the back of this paper in PLOS One:

I think that they have been rather uncritical and so have sent TWiM this email. What do you think?

Hi Vincent et al

I have been listening to TWiM for several weeks after moving to a new job that requires me to undertake a one-hour drive to work. I enjoy the show very much: in fact, I enjoy it so much that I am thinking of setting up a similar podcast this side of the Atlantic.

But this is not the reason I am writing.

I listened to your discussion of the brain microbiome this week. And, even though I note the question mark in your title after the term "brain microbiome", I think you were not skeptical enough.

OK, I admit that the paper presents an internally consistent story. But they don't report trying to grow the bacteria. And, rather than one organism, they would have us believe there is a kitchen sink's worth of microbes in these brains. Remember when we look at most sterile samples, we assume that a mixed growth equals contamination! And alpha-proteobacteria are common contaminants of water supplies, even in the International Space Station! http://www.ncbi.nlm.nih.gov/pubmed/16364606

But more generally, as Carl Sagan put it, extraordinary claims require extraordinary evidence! And IMHO the evidence presented here is not compelling enough to overturn over a century of microbiology and histopathology. If these bacteria are really there, would we not have seen them already? If we look at precedents, we could be looking at the next Helicobacter pylori and these authors are going to be Nobel laureates. But I think a more plausible precedent is XMRV or arsenic life, both of which turned out to be nonsense. Go take a look at Ioniddis' paper "Why most published research findings are false" http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.0020124

Only time and attempts at independent replication will tell what is going on here. But I am prepared to wager that in ten years time this paper will have been discredited or forgotten.

Keep up the good work!

Cheers

Mark

Professor Mark Pallen


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