IBS: Bacterial Infection and Dysbiosis

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Irritable bowel syndrome, or IBS, is a common gastrointestinal disorder. One paper cites anywhere between 3-20% of the population suffers from IBS.

As the diagnosis irritable bowel syndrome is simply a description of the symptoms it’s clear that we haven’t quite nailed down what is actually causing the upset.


Definition and Symptoms of IBS

The American Journal of Gastroenterology publication on IBS defines it as the following

“IBS is a chronic illness of disordered bowel function and abdominal pain or discomfort that is distinguished by the absence of biochemical markers or structural abnormalities (1).

Symptoms include (2).

  • Abdominal pain relieved with defecation
  • Bloating
  • Altered stool frequency and form – loose to hard/constipated
  • Abdominal distention

The ROME II criteria is most frequently used in the papers that I see regarding IBS diagnosis.

MDCALC provides an interesting score card to test the possible diagnosis of IBS


IBS and Dysbiosis – Imbalanced Gut Causing Symptoms 

Dysbiosis, or microbial imbalance, is prevalent in a whole range of different disease states, yet another connection between gut health and overall health.

There have been many scientific enquiries into the connection between dysbiosis and IBS with some interesting findings.

One trial took 165 healthy controls and established a healthy baseline, or a “normal” microbiota. They then compared that baseline to 330 people, some with IBS some with IBD and also healthy volunteers.

From the baseline they found 73% of IBS patients to have a disrupted or dysbiotic microbiota, 70% in treatment-naive IBD patients, 80% in IBD patients in remission and only 16% in the healthy individuals.

The interesting aspect of the study is the differences between the IBD and the IBS microbiota.

The bacteria contributing to dysbiosis within the IBS group were

  • Proteobacteria (Shigella/Escherichia) – elevated
  • Ruminococcus gnavus – elevated

Dysbiosis in the IBD group presented as

  • Proteobacteria (Shigella/Escherichia) – massively elevated
  • Firmicutes, specifically F. prausnitzii – decreased growth
  • Bacteroidetes (Bacteroides and Prevotella) – decreased growth

Here we can see an interesting correlation between the IBS and IBD groups. The elevation of the proteobacteria phylum. Unfortunately in many cases they didn’t drill down to the actual species. The proteobacteria phylum contain many pathogenic bacteria including members of the Escherichia, Salmonella, Vibrio, Helicobacter and Yersinia genera.

Is bacterial infection driving dysbiosis resulting in the irritable bowel syndrome symptoms? Something to consider.     

One important note in the dysbiotic IBD group is the decreased growth of Faecalibacterium prausnitzii. I have been hearing more and more about Faecalibacterium prausnitzii. This is a friendly resident in our digestive tract making up more than 5% of the total bacterial population in a healthy human microbiome with some harbouring up to 15% of the microbe (5).

Either way that equates to the highest level of one particular species of bacterium in residence.

As one of the most abundant butyrate producers Faecalibacterium prausnitzii contributes many advantageous benefits including (5)

  • protection against pathogen invasion
  • modulation of immune system
  • reduction of cancer progression
  • anti-inflammatory activities in the colon mucosa

On the same subject, another study looked at the difference between patients with psoriasis, IBD and healthy controls. They found significantly decreased levels of Faecalibacterium prausnitzii in both the psoriasis and the IBD group which correlates with the previous study.

There must be a connection between the inflammatory aspect of IBD and the decreased presence of such a prolific butyrate producer as F. prausnitzii.


SIBO – Is This The Real Root Cause of IBS?

As there are at least two meta-analysis level reviews (top level science analysing and presenting findings from many trials) I’m sure there will be a SIBO and IBS article coming here sooner or later.

For now I thought it was worth mentioning.

From a review referencing the meta-analysis  between 31-54% of IBS patients tested positive for SIBO (variation depended on the breath test used) This was from quite a large pool of irritable bowel patients 1921 in total. Quite an impressive finding and worth considering if you are suffering from IBS complaints. 


Gut Testing

GI testing, preferably a combination of a Comprehensive Stool Analysis and a PCR (DNA based) test would be highly recommended as well as a SIBO breath test.

Depending on where you live your doctor can order you the PCR based testing. This will screen for some of the common pathogens (both bacteria and parasites). What it won’t screen for is yeast infections, such as candida, opportunistic bacterial overgrowth (a great example here would be Klebsiella infections) and an imbalanced gut ecosystem, as seen in many inflammatory bowel disease cases.

More info on GI testing here


References and Resources

  1. An Evidence-Based Systematic Review on the Management of Irritable Bowel Syndrome
  2. Diagnosis of irritable bowel syndrome.
  3. https://www.mdcalc.com/rome-ii-diagnostic-criteria-irritable-bowel-syndrome-ibs
  4. Deviations in human gut microbiota: a novel diagnostic test for determining dysbiosis in patients with IBS or IBD
  5. Faecalibacterium prausnitzii and human intestinal health
  6. Similar Depletion of Protective Faecalibacterium prausnitzii in Psoriasis and Inflammatory Bowel Disease, but not in Hidradenitis Suppurativa
  7. Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome: A Bridge between Functional Organic Dichotomy
  8. Recommended GI testing – CDSA + PCR

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