Do SIBO Symptoms Differ by Type of Bacterial Overgrowth?

While SIBO symptoms may not vary according to bacteria type, researchers found differences in iron deficiency.

Researchers found no significant difference in small intestinal bacterial overgrowth (SIBO) symptoms when comparing aerodigestive tract (ADT) and colonic-type bacteria. The study findings were published in Digestive Diseases and Sciences.

The researchers conducted a single-center, prospective comparison study of 69 participants aged 18 years and older with enteroscopy-confirmed SIBO from March 2013 to November 2019. The study objective was to determine if clinical symptoms of SIBO differed based on type of bacterial overgrowth present. None of the eligible participants took probiotics, antibiotics, or bowel prep within the preceding 30 days.

The researchers compiled a list of clinical characteristics, risk factors, and lab results for each participant. The Patient Assessment of Gastrointestinal Disorder-Symptoms Severity Index (PAGI-SYM) was used to quantify symptom severity for gastroesophageal reflux, gastroparesis, and functional dyspepsia.

Each participant underwent proximal jejunal luminal aspiration and mucosal biopsy via upper enteroscopy to obtain samples for laboratory culturing and analysis to determine the predominant strain of bacteria responsible for SIBO.

[W]e were able to demonstrate differences in iron deficiency and underlying risk factors between ADT and colonic-type SIBO.

ADT SIBO involved more than 105 CFU/mL of oropharyngeal and respiratory bacteria, including Diptheroids, Enterococcus, Fusobacterium, Lactobacillus, Micrococcus, Peptostreptococcus, Staphylococcus, Streptococcus, or other strains.

Colonic-type SIBO involved more than 104 CFU/mL of distal small bowel and colon bacteria, including Acinetobacter, Bacteroides, Citrobacter, Clostridium, Enterobacter, Escherichia, Klebsiella, Neisseiria, Proteus, or other strains.

Mucosal biopsy evaluated the samples for villous atrophy, H pylori, intraepithelial lymphocytic infiltration, or additional abnormalities.

The researchers found that daily abdominal distention occurred more frequently in patients with ADT SIBO, compared with colonic-type SIBO (65.2% vs 39.1%, P =.09). Iron deficiency also occurred more frequently in patients with ADT SIBO, compared with colonic-type SIBO (33.3% vs 10.3%, P =.04).

The researchers also compared prevalence of certain risk factors for developing either ADT SIBO or colonic-type SIBO. Patients with ADT SIBO were more likely to demonstrate the risk factor for diminished gastric acid, compared with those who had colonic-type SIBO (91.3% vs 67.4%, P =.02).

Patients with colonic-type SIBO were more likely to demonstrate risk factors promoting colonic bacterial colonization, such as failure of small bowel motility (P =.12), ileocecal valve resection (P =.24), and discontinuous small bowel (P =.01), although only the latter risk factor reached statistical significance.

A post hoc analysis of 32 participants who did not have any known risk factors for SIBO revealed that nausea or vomiting (P =.047) and lower abdominal pain (P =.027) occurred more in those with colonic-type SIBO than ADT SIBO.

“[W]e were able to demonstrate differences in iron deficiency and underlying risk factors between ADT and colonic-type SIBO,” study authors wrote. “However, a distinct clinical profile remained elusive. Many of our subjects had underlying conditions that may have affected the gastrointestinal tract complicating our results.”

Study limitations include risk of contamination of the catheter used for aspiration and challenges surrounding sterile collection of small bowel samples, sampling only one location in the jejunum which may not fully represent the bacterial composition of the entire small intestine, exposure of anaerobic cultures to aerobic environments, and the potential inability of jejunal culturing to detect all intestinal bacterial species representing only the cultures that grew.

Additionally, participants may have had underlying comorbidities that confounded results. The study used an outcome measure (PAGI-SYM) that was not validated for upper GI symptoms associated with SIBO, which may have affected accuracy of symptom profiling for ADT vs colonic-type SIBO.

Disclosures: One study author declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original source for a full list of the author’s disclosures.


Siddique DA, Jansson-Knodell CL, Gupta A, et al. Clinical presentation of small intestinal bacterial overgrowth from aerodigestive tract bacteria vs colonic-type bacteria: a comparison study. Dig Dis Sci. 2023;68(1):3390-3399. doi:10.1007/s10620-023-07999-x