Lasting Effects of Helicobacter pylori Infection on the Microbial Communities of Patients with and without Small Intestinal Bacterial Overgrowth.

Gastrointestinal (GI) microbial populations are important in maintaining normal functioning of the GI by preventing disorders. Dysbiotic microbiota may increase the likelihood of small intestinal bacterial overgrowth (SIBO), a syndrome associated with significant morbidity. We aimed to inves- tigate the microbiota populations of patients with SIBO. Patients with symptoms of SIBO were consecutively enrolled; they underwent a SIBO hydrogen breath test and stool was collected for microbiome analysis by sequencing of the 16S rRNA. Of the 55 patients recruited, 42 (76.4%) were positive for SIBO. When visualizing the bacterial β-di- versity, a sub-cluster of patients was identified. Further examination of these patients' records re- vealed previous treatment for Helicobacter pylori (HP). Microbiome analysis of these patients demonstrated a significant decrease in β-diversity (p-value<0.001) compared to patients without previous HP therapy. Furthermore, β-diversity was significantly different in this subgroup, and sev- eral bacterial taxa were differentially expressed, including one from the genus Methanobrevibacter, which was reduced in patients that previously underwent HP treatment. Our findings suggest that while symptoms associated with SIBO may cause dysbiosis, there was no differentiation in fecal microbiome composition based on SIBO diagnosis. Furthermore, our results support previous observations regarding antibiotic-altered microbiota with effects extending two and three years post-treatment.