Fecal Transplant Fails to Decolonize Resistant Bacteria in GI Disease

The Challenge of Intestinal Multidrug-Resistant Colonization

The human gut serves as a critical reservoir for antimicrobial resistance genes, where dysbiosis (a pathological imbalance in microbial composition and function) often facilitates the proliferation of multidrug-resistant organisms [1, 2]. For patients with chronic gastrointestinal conditions, this colonization significantly increases the risk of invasive infections, healthcare-associated transmission, and overall mortality [3, 4]. While fecal microbiota transplantation (the transfer of screened donor stool into a recipient's gastrointestinal tract to restore microbial ecology) has become a standard intervention for recurrent Clostridioides difficile infection, its utility in eradicating other resistant pathogens remains a subject of active clinical investigation [5, 6, 7]. Current evidence regarding the efficacy of microbial restoration for decolonization is inconsistent, as meta-analyses of randomized trials have shown no significant effect on short-term (RR=1.18; 95% CI 0.81-1.71) or long-term decolonization rates [3, 8]. A recent randomized, sham-controlled trial involving 114 patients now provides rigorous data on whether this approach can effectively clear resistant strains in high-risk populations [9].

Trial Design and High-Risk Patient Characteristics

Researchers conducted a randomized, double-blind, sham-controlled clinical trial at a tertiary care center in India, recruiting participants from gastroenterology wards and intensive care units. The study targeted a high-risk population with persistent colonization by multidrug-resistant organisms (MDROs), defined as bacteria resistant to three or more antimicrobial classes. Patient recruitment occurred between July 2022 and June 2024, with data analysis concluding in April 2025. The study randomized 114 patients with a mean age of 40.6 years (SD 12.5), of whom 80 (70.2%) were male. The cohort presented with significant underlying morbidity: 52 patients (45.6%) had pancreatitis and 43 patients (37.7%) had cirrhosis, conditions often associated with increased intestinal permeability and frequent antibiotic exposure. To isolate the biological effect of the donor microbiota, 58 patients received fecal microbiota transplant (FMT) via colonoscopy, while 56 patients received a sham intervention consisting of sigmoidoscopy with saline injection. At baseline, the prevalence of highly resistant pathogens was nearly universal: 55 patients (94.8%) in the FMT group and 56 patients (100%) in the sham group were colonized with carbapenem-resistant Enterobacteriaceae or extended-spectrum β-lactamase–producing Enterobacteriaceae. These pathogens are particularly concerning in clinical practice because they produce enzymes that hydrolyze most beta-lactam antibiotics, often leaving clinicians with few viable therapeutic options.

Primary Outcomes and Decolonization Efficacy

The primary objective was to evaluate decolonization efficacy using an intention-to-treat analysis (a statistical approach that includes every participant who was randomized, regardless of whether they completed the protocol, to prevent bias). Although five patients were lost to follow-up (two in the FMT group, three in the sham group), the final results demonstrated that the intervention failed to meet its primary endpoints. At the four-week assessment, MDRO decolonization occurred in 18 patients (31.0%) in the FMT group compared to 17 patients (30.4%) in the sham group. This resulted in an absolute difference in decolonization of only 0.6% (95% CI, −16.2% to 17.6%; P = .94), indicating that the microbial transplant was no more effective than a saline injection for clearing resistant strains. Furthermore, the total burden of antimicrobial resistance genes (the specific genetic sequences, such as blaNDM or blaKPC, that confer resistance to antibiotics) remained unchanged. The researchers found no significant difference in the number of resistance genes at four weeks, with a median of 2.5 genes (IQR, 1.2 to 3.0) in the FMT group versus 2.0 genes (IQR, 1.0 to 3.0) in the sham group (P = .68). While the intervention did not achieve decolonization, the safety profile was reassuring: adverse events within the four-week follow-up period were comparable between the two groups, suggesting that the lack of efficacy was not due to poor tolerability or procedural complications.

Impact on the Gut Microbiome, Virome, and Mycobiome

To understand why the clinical decolonization failed despite the introduction of donor microbiota, the researchers performed 16S ribosomal RNA gene sequencing (a technique that identifies bacterial genera by sequencing a specific, conserved genetic marker) on 71 patients. The analysis revealed that while a single session of FMT modulated gut microbiome diversity and composition, these changes were insufficient to displace established MDROs. Specifically, the FMT group showed an enrichment of bacteria capable of producing short-chain fatty acids, such as butyrate, which are essential for maintaining the colonic mucosal barrier and modulating local immune responses. These beneficial microbial alterations were entirely absent in the sham group. The study also utilized viruslike particles shotgun sequencing (a method that sequences all viral genetic material in a sample to map the virome) and found that viral diversity remained unchanged after FMT. Similarly, the researchers examined the mycobiome (the fungal community within the gut) using ITS2 sequencing (a technique targeting the internal transcribed spacer 2 region to identify fungal species). This analysis showed that FMT induced only modest, transient alterations in the gut mycobiome. For the practicing clinician, these findings suggest that the 'colonization resistance' required to oust MDROs may require more intensive or frequent dosing than a single transplant, as the existing resistant bacterial community, virome, and mycobiome appear highly resilient to a one-time microbial challenge.

References

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