Relapsing-remitting MS patients may have less diverse gut bacteria
Study: Specific bacterial groups increase despite lower overall diversity
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People with relapsing-remitting multiple sclerosis may have less diverse gut bacteria (pictured) than healthy people, according to a study. (Photo from iStock)
- People with relapsing-remitting MS exhibit significantly lower gut bacteria richness and diversity compared to healthy individuals.
- Patients show selective alterations in microbial composition, including increased abundance of specific bacterial genera.
- Changes involve shifts in active bacterial genes rather than broad taxonomic variations.
People with relapsing-remitting multiple sclerosis (MS) may have less diverse gut bacteria than healthy people, with shifts in genes involved in how well certain bacteria break through the body’s defenses, according to a study.
The findings add to growing evidence that changes in the microbiota may be linked to the disease.
The study, “Significant changes in the fecal bacteriobiota richness and diversity in patients with relapsing-remitting multiple sclerosis compared to healthy individuals,” was published in the European Journal of Clinical Microbiology & Infectious Diseases by a team of researchers in Poland.
PPMS patients had lower bacterial richness and diversity
MS occurs when the immune system mistakenly attacks the protective covering of nerve fibers, causing inflammation and damage in the brain and spinal cord. Gut microbiota — the community of microorganisms living in the digestive tract — appear to play an important role in MS, but exactly how remains unclear.
“The gut microbiota plays a key role in the regulation of immune responses and has been implicated in the pathogenesis [disease-causing mechanisms] of multiple sclerosis, particularly through its role in immune system modulation and maintenance of intestinal homeostasis [health],” the researchers wrote.
This study looked at how the gut bacteria of people with relapsing-remitting MS, a form of the disease in which symptoms worsen during relapses and then ease or disappear for some time, differ from those of healthy people. It included 126 stool samples, 68 from people with relapsing-remitting MS and 58 from healthy people, who were used as controls.
To identify the different bacteria present in the stool samples, the researchers used a method called 16S rRNA gene sequencing. This method examines specific, conserved regions of bacterial genetic material within the 16S ribosomal RNA gene. The study focused on the V3-V4 regions of this gene.
The broad structure of the gut microbiota was similar in both groups. Firmicutes and Bacteroidota were the most common bacterial groups, called phyla, in both patients and controls. Actinobacteriota was the third most common phylum. At the genus level, which is a lower-level classification compared with phylum, Bacteroides and Faecalibacterium were the most abundant bacteria in both groups.
However, patients had lower bacterial richness and diversity. Richness refers to the number of different bacteria detected, while diversity also considers how evenly those bacteria are represented. The number of observed amplicon sequence variants, which are closely defined genetic sequences used to tell one bacterial group from another, was significantly lower in patients.
These findings indicate that [relapsing-remitting MS] is associated with selective alterations in gut microbiota composition and shifts in the distribution of E. coli virulence-related genes rather than broad taxonomic [classification group] changes.
The researchers also examined beta diversity, which describes differences in the overall bacterial community between individuals or groups. Using Bray-Curtis dissimilarity to measure how stool samples differed from each other, they found patients and controls differed significantly. However, the groups overlapped considerably in a visual method for displaying similarities and differences between microbial communities.
While patients also showed greater variation from one person to another, a detailed analysis identified seven bacterial genera that were significantly more abundant in patients than in controls. These were Lactobacillus, UBA1819, Escherichia-Shigella, Eubacterium fissicatena, Eisenbergiella, Streptococcus, and Clostridium innocuum.
The researchers also looked at certain genes in Escherichia coli bacteria that are linked to virulence, or the degree to which a bacterium can cause disease and infect the host. The total median number of E. coli virulence-associated genes detected did not differ between the two groups (1.5 genes vs. 2 genes).
However, the distribution of individual genes was different. The fimG/fimH and papC genes, which are involved in attachment to surfaces, were more active in patients, while cnf1 and hlyA, which are involved in production of toxins, were more active in controls. This suggests that the difference was not in the overall number of virulence-associated genes, but in which specific genes were active.
“These findings indicate that [relapsing-remitting MS] is associated with selective alterations in gut microbiota composition and shifts in the distribution of E. coli virulence-related genes rather than broad taxonomic [classification group] changes,” the researchers concluded.
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