Gastrointestinal system

Dysbiosis
On average, ME/CFS patients have lower levels of Bifidobacteria, Escherichia coli and higher levels of aerobic bacteria. , in particular Enterococcus and Streptococcus species. The latter produce D-lactate, a form of lactic acid only produced by non-human cells that is poorly metabolized in humans. D lactate is associated with a wide variety of cognitive and neurological symptoms, such as in patients who suffer from D lactate acidosis. A study found that higher levels of enterococcus bacteria in CFS patients were associated with more severe neurological and cognitive dysfunction.

Intestinal permeability
In a healthy digestive tract, the intestinal walls provide a tight, selective barrier to allow the absorption of nutrients prevent the entry of bacteria or pathogens. However, in CFS patients, there is evidence of increased intestinal permeability. One study found higher levels of serum IgA and IgM against lipopolysaccarides (LPS), a major component of the outer membrane of gram negative bacteria. . Serum IgA was significantly correlated to the severity of illness.