Differences in Bacteria, Viruses in MS Patients’ Guts Seen in Study

Levels of more than 60 species of bacteria altered with the disease

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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An illustration of bacteria.

The amounts of more than 60 species of bacteria are altered in the gut in people with multiple sclerosis (MS) compared with those without the disease, a new study reports.

Researchers also identified differences in the makeup of viruses that infect gut bacteria in patients, which they said may be promising avenues for future treatment strategies.

The study, “The gut microbiota in multiple sclerosis varies with disease activity,” was published in Genome Medicine.

The human digestive system is home to billions of bacteria and other microorganisms, collectively known as the gut microbiome. These symbiotic microbes can have profound effects on health and disease, but their roles in MS are still largely unknown.

Here, researchers analyzed stool samples to compare the composition of the gut microbiome in 148 people with MS and a matched group without any known disease (controls). All were identified as white Danish.

Among the MS patients, 86% had relapsing-remitting disease and the rest had clinically isolated syndrome. About two-thirds of the patients were on treatment, while 36% had never been treated. More MS patients than controls were smokers (27% vs. 10%).

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High Levels of Gut Bacterial Toxins Found in Spinal Fluid of MS Patients

Higher, lower levels gut bacteria in MS patients

Gut microbiome analyses showed that bacterial diversity was generally comparable in MS patients and controls. However, the researchers noted that MS patients on treatment showed less diversity than controls or patients who’d never been treated, suggesting “that global differences in [bacterial] diversity might be due to treatment of multiple sclerosis.”

The researchers identified 61 species of bacteria present at significantly altered levels in the MS patients compared with the controls. Specifically, 31 bacteria were more abundant in MS patients, while the other 30 were lower. Several of these species, including Clostridium leptumClostridium inocuumAnaerotruncus colihominis, and Ruminococcus gnavus, have been linked with MS in previous reports, they noted.

Levels of many of these MS-associated bacteria showed statistically significant correlations with markers of inflammation measured in the blood. For example, the bacterial species Flavonifractor plautii, found to be more abundant in MS patients, was associated with higher levels of the inflammatory marker C-reactive protein (CRP) and higher counts of white blood cells (leukocytes). This association was seen both in MS patients and in controls.

Analyses of 31 MS patients who weren’t on treatment showed that those with more bacterial richness in the gut microbiome were significantly more likely to have a relapse during the two years of follow-up after samples were collected. However, differences in gut microbiome richness showed no clear association with disease activity in treated patients.

“In treatment-naïve cases, we found a strong and positive relationship between the number of relapses during [two] years of follow-up and bacterial richness, meaning that cases with clinical disease activity were richer in gut bacteria than clinically not active patients,” the researchers wrote. “This result is unexpected since a high gut bacterial richness is commonly considered as a beneficial marker of health.”

The scientists also analyzed viral gut microbiota — the viruses that infect bacteria in the digestive tract. Notable differences between the MS patients and the controls were seen, and patients tended to have lower levels of a virus called EFC-1, which was linked with a greater activity of pro-inflammatory genes.

The EFC-1 virus normally infects and kills cells of the bacterial species Enterococcus faecalis, which is known to be an opportunistic pathogen. The bacteria doesn’t normally cause problems, but under some conditions — such as if the immune system is weakened or impaired — it can cause severe infections.

Lower levels of the EFC-1 virus could allow more of these bacteria to grow, which might contribute to health problems in MS, the researchers said.

“Therefore, an enrichment of [EFC-1] might be considered a potential target for future explorative intervention in multiple sclerosis,” they wrote.

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