“Porphyromonas gingivalis is the only bacterium known to do that,” Dr. Lorber said. “The idea here is that this organism, in genetically susceptible individuals, makes citrullinated antigens that then serve as systemic immunogens, resulting in rheumatoid arthritis.”
The Microbiome
Research in heart disease has found that, after inoculating human cells with Chlamydophila pneumonia, the bacterium up-regulates genes with important pro-inflammatory functions, including those associated with atherosclerosis.
Another shift is occurring, too, Dr. Lorber said. Ever since anthrax was proved to be caused by bacteria, more than a hundred years ago, there was a belief that one disease was caused by one organism. But that might not always be the case, new evidence is showing.
“It may not be one organism,” Dr. Lorber said. “It may be populations of organisms or relative proportions of populations. So maybe it’s not infection in the traditional sense. Maybe it’s an imbalance of the microbiome,” or “dysbiosis.”
For example, using new tools, such as 16S sequencing—a way to assess the taxonomy in difficult-to-study microbiomes—in people with RA and in controls, researchers have found that the presence of Prevotella copri bacteria, with an associated reduction in the normal Bacteroidetes population, is correlated strongly with new onset of RA.2
Scientists are also shedding light on the so-called “gut–brain axis,” signaling in which the gut talks to the brain through neural mechanisms, including the vagus nerve, as well as endocrine mechanisms, immune mechanisms and metabolic mechanisms.
Germ-free mice that are deliberately stressed develop higher levels of stress hormone, as well as lower levels than normal mice of a brain protein that modulates synaptic growth and transmission.3
“If you recolonize with normal mice gut flora, you can reverse that and they lower levels of stress hormones,” Dr. Lorber said.
Obese people, researchers have found, have more Bacteroidetes and fewer Firmicutes than controls who are lean.4
“It turns out that obese individuals who complain all the time (that), ‘I ate the same thing you ate—why don’t you get fat?’ may have a good explanation,” Dr. Lorber said. “They may have more efficient energy harvesting from what they eat.”
‘I think it’s very likely that as time goes by we will establish firmer links between transmissible agents & chronic illness. That’s exciting because it opens the opportunity for prevention through immunization.’ —Bennett Lorber, MD, MACP
Future Possiblities
All of these discoveries are cause for great optimism, he said.
“I really think we may soon be treating neuropsychiatric disorders with probiotics,” Dr. Lorber said. “The hard part is being able to figure out which probiotic is going to do the trick. But just imagine this.
