## 5 _C. jejuni's Role in Shaping Microbiota and Contributing to PI-IBS
Conversely, in patients with diarrhea-predominant IBS-D, there appears to be a connection between the presence of both Gram-positive and Gram-negative bacteria and the levels of C-X-C motif chemokine ligand 11, a chemokine involved in inflammatory responses. [PERSON] and colleagues recently compared the efficacy of fecal microbiota transplantation (FMT) against traditional pharmacotherapy in patients with PI-IBS, and FMT demonstrated notable effectiveness, safety and tolerability [16]. PI-IBS, often triggered by infections leading to gut microbiota disturbances, is typically managed initially with non-absorbable antibiotics, like infaximin-\(\alpha\), or probiotics to amend the microbiota imbalance [16]. However, this research highlighted the superior outcomes of a single FMT session, benefiting over 60% of PI-IBS patients--a success rate aligning with a standard 4-week pharmacotherapy regimen. The study also revealed a significant presence of potentially pathogenic bacteria such as _Staphylococci_, _Streptococci_ and various strains of _E. coli_, _Klebsiella_ spp., _Proteus_ spp. and _Enterobacter_ spp. in PI-IBS patients' feces. Notably, both treatment groups exhibited a marked reduction in intestinal dysbiosis frequency and severity one month post-treatment, with the FMT group showing significantly better outcomes. Furthermore, FMT led to a favorable shift in the gut microbiome composition, notably increasing _Firmicutes_ and _Bacteroidetes_ levels, which normalized solely in FMT-treated patients. This group also saw normalization in Actinobacteria levels and other conditionally pathogenic flora, unlike the standard care group, which only demonstrated a tendency toward such changes. The exceptional microbiological efficiency of FMT in PI-IBS patients might be attributed to the altered metabolic activity of the gut microbiota stimulated by the high concentration of regulatory molecules and metabolites in the donor feces. This metabolic shift notably boosts the levels of _Firmicutes_ and _Bacteroidetes_ and the production of short-chain fatty acids, especially butyrate, contributing to therapeutic benefits [16]. Otherwise, a decrease in anaerobic metabolites, notably short-chain fatty acids and secondary bile acids, increases the colonic lumen's pH [64]. This shift in pH can compromise colonization resistance, a mechanism that helps to prevent the overgrowth of harmful microbes in the gut. Consequently, this altered environment may facilitate the proliferation of pathogens and members of the _Proteobacteria_ phylum, including facultative anaerbles like _Enterobacteriaceae_[64]. Specifically, in poultry abattoir workers, who are at a higher risk of infection with _Campylobacter_, an elevation in bacteria from the _Bacteroidetes_ phylum (i.e., _Bacteroides_ and _Prevotella_) was noted--a characteristic similarly observed in PI-IBS patients but not in those with IBS, who typically show an increased ratio of _Firmicutes_ to _Bacteroidetes_[10; 27; 65]. On the other hand, travelers who develop infectious diarrhea exhibit low levels of _Bacteroidetes_, hinting at a potential protective role of this phylum. Interestingly, the likelihood of developing PI-IBS following traveler's diarrhea is two times lower than after other forms of gastroenteritis, suggesting differential impacts of microbial composition on the risk and nature of gastrointestinal infections [27]. Furthermore, previous authors have noted the depletion of the _Subdoligranulum variable_ in PI-IBS, a butyrate-producing bacterium, which has been shown to induce the production of interleukin IL-18, a proinflammatory cytokine, in biopsy samples from PI-IBS patients but not in samples from healthy individuals [27; 66]. Conclusively, this highlights a unique response of the host's immune system to a normally symbiotic microbe under pathological conditions, suggesting a nuanced and dual-natured interaction with the microbiota.