A small study conducted in the US has found that the bacteria living in the throats of schizophrenic patients were significantly different from those in healthy volunteers. While the discovery suggests a difference in how the immune system is functioning across the schizophrenic and control groups, at this stage, scientists aren't entirely sure what this means

"The role of the human microbiome in schizophrenia remains largely unexplored," they report in the journal Peer J. "The microbiome has been shown to alter brain development and modulate behaviour and cognition in animals through gut-brain connections, and research in humans suggests that it may be a modulating factor in many disorders."

The team from George Washington University took throat swabs of 32 patients - half of which had been diagnosed with schizophrenia. After sequencing the genomes of the bacterial colonies that were living in the throats of their volunteers, "high-level differences were evident at both the phylum and genus levels", they report, with Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria dominating both schizophrenic patients and controls, and Ascomycota being more abundant in the schizophrenic patients than the controls. 

They also found that the controls were playing host to a greater diversity of bacteria, and lactic acid bacteria were more abundant in the schizophrenic patients, including species of Lactobacilli and Bifidobacterium, which have been shown to modulate chronic inflammation. 

As the bacteria found in our throats start out in our guts, the results fit into the increasing body of research that suggests a link between our brain function and our gut microbiomes. And that's not exactly surprising - 90 percent of the human body is made up of microorganisms, and they contain around 100 times the number of genes in the human genome, accumulatively weighing approximately the same as a human brain.

Last year, researchers in Ireland also looked into how these bugs could be affecting people with schizophrenia and the results of their preclinical investigations indicated that, "these microbes majorly impact on cognitive function and fundamental behaviour patterns, such as social interaction and stress management," according to the paper published in Molecular Psychiatry. "We are pivotally dependent on the neuroactive substances produced by such bacteria," the researchers concluded.

So how could bacteria that move from our guts to our throats have an effect on our brains? It's not yet clear, but we do know that the immune system appears to be weaker in schizophrenic patients, which could explain the difference in species in the most recent study, and recent research has shown that the bacteria living in us can have an effect on our moods. 

A much larger study that also analyses bacteria taken directly from the guts of schizophrenic and healthy patients would be needed for a more definitive answer to emerge, but the study does point to the possibility of a more accurate test for schizophrenia being based on bacterial swabs, as Alexandra Ossola writes at Popular Science:

"If future studies reveal specific, universal differences between schizophrenic and non-schizophrenic patients, doctors could find biomarkers in the microbiome to diagnose patients more quickly and accurately. If researchers can also understand the mechanisms for how the bacteria cause or exacerbate the disease (uncovering causation, not just correlation), they could also find new treatments for schizophrenia."

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