🦠 microbiology

Longitudinal Changes in Nasal and Oral Microbiome and Antimicrobial Resistance Gene Profiles in Response to Human Fecal Microbiota Transplantation

This longitudinal study demonstrates that fecal microbiota transplantation for recurrent *Clostridioides difficile* infection not only restores gut microbial diversity but also induces significant, albeit partially transient, shifts in the nasal microbiome and antimicrobial resistance gene profiles, providing evidence for systemic gut-lung axis interactions while leaving the oral microbiome largely unaffected.

Original authors: Vallecillo-Zuniga, M. L., Akeefe, A., Brown, D. G., Wahlig, T. A., Marchetti, M., Heiner, T., Davis, K. L., Nieznanski, C., Flynn, A., Leung, D. T.

Published 2026-01-28

📖 3 min read☕ Coffee break read

CC BY 4.0

Original authors: Vallecillo-Zuniga, M. L., Akeefe, A., Brown, D. G., Wahlig, T. A., Marchetti, M., Heiner, T., Davis, K. L., Nieznanski, C., Flynn, A., Leung, D. T.

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

Imagine your body as a bustling city with different neighborhoods. The gut is the main industrial district, while the nose and mouth are like the city's air intake and ventilation systems. Scientists have long suspected that these neighborhoods talk to each other through invisible pipes called the "gut-lung axis," but they haven't fully understood how fixing a problem in the industrial district affects the air intake.

This study decided to test that connection by treating patients with a "reset button" for their gut called Fecal Microbiota Transplantation (FMT). Think of FMT as swapping out a clogged, malfunctioning sewer system with a fresh, healthy one to cure a stubborn infection.

Here is what happened when the researchers watched the city's neighborhoods over time:

1. The Gut Gets a Makeover
First, the treatment worked exactly as intended in the gut. The "industrial district" became more diverse and balanced. The bad actors—specifically troublemakers like Klebsiella and E. coli—were pushed out, while the helpful residents (Bacteroidota) moved in and took over.

2. The Nose Gets a Surprise Upgrade
Here is the fascinating part: even though the treatment was only given to the gut, the nose (the upper respiratory tract) changed too. It's as if fixing the sewer system automatically cleaned the air filters.

The nose became less crowded with a chaotic mix of bacteria.
The "good" bacteria (Moraxella) grew stronger.
Crucially, the dangerous "villains" that often cause lung infections, like Staphylococcus aureus and Streptococcus pneumoniae, started to leave the neighborhood.
By the end of the study (Day 56), the nose's bacterial community had mostly returned to a healthy, balanced state, similar to people who never needed the treatment.

3. The "Superbugs" Lose Their Weapons
The researchers also looked at the "weapons" these bacteria carry, known as antibiotic resistance genes (ARGs). Think of these as shields that make bacteria immune to medicine.

Before the treatment, the nose was full of bacteria with shields against common drugs like penicillin and fluoroquinolones.
After the gut treatment, these shields in the nose started to disappear. By Day 56, the nose had as few "superbug shields" as a healthy person's nose.

4. The Mouth Stays the Same
Interestingly, the mouth didn't change much. It remained stable, like a quiet suburb that wasn't affected by the construction happening in the industrial district or the air filters in the nose.

The Big Takeaway
This study shows that when you fix the gut, you don't just fix the gut. It sends a ripple effect through the body, cleaning up the nose and disarming the bacteria there. It proves that the gut and the lungs are deeply connected, like neighbors who share a single water supply: when you clean the water at the source, the water in the neighbor's house gets cleaner, too.

Technical Summary: Longitudinal Changes in Nasal and Oral Microbiome and Antimicrobial Resistance Gene Profiles in Response to Human Fecal Microbiota Transplantation

Problem Statement
While the "gut-lung axis" is recognized as a framework describing interactions between intestinal and respiratory mucosal systems via microbial, metabolic, and immune pathways, the systemic impact of gut-targeted therapies on upper respiratory tract (URT) communities remains underexplored. Specifically, there is a lack of longitudinal data regarding how fecal microbiota transplantation (FMT), a therapy primarily used for recurrent Clostridioides difficile infection (CDI), influences the composition of the nasal and oral microbiomes and their associated antimicrobial resistance (AMR) profiles.

Methodology
The study employed a longitudinal design involving adult patients undergoing FMT for recurrent CDI, alongside a cohort of healthy controls. The experimental protocol included the collection of fecal, nasal, and oral samples at three distinct time points: baseline (Day 0), and follow-ups at Day 14 and Day 56 post-FMT.

The core analytical technique was shotgun metagenomic sequencing. This approach was utilized to:

Quantify microbial diversity and taxonomic composition across all sample types.
Profile the abundance and diversity of antimicrobial resistance genes (ARGs).
Compare the trajectories of the FMT cohort against healthy controls to distinguish treatment-specific effects from natural variation.

Key Results
The study identified distinct, time-dependent shifts in microbial ecology and resistome profiles following FMT:

Gut Microbiome: FMT successfully restored gut diversity and reduced the abundance of key intestinal pathobionts, specifically Klebsiella spp., Escherichia spp., Shigella spp., and Klebsiella pneumoniae. At the phylum level, fecal Bacteroidota increased, while Mucoromycota decreased.
Nasal Microbiome: Significant alterations were observed in the nasal cavity. Post-FMT changes included a reduction in overall richness and diversity, an expansion of Moraxella, and a decrease in taxa associated with respiratory colonization, notably Staphylococcus aureus and Streptococcus pneumoniae. By Day 56, these nasal communities showed partial recovery toward profiles resembling those of healthy controls.
Oral Microbiome: In contrast to the gut and nasal sites, the oral microbiome and its resistome remained largely stable throughout the study period, exhibiting only minor fluctuations and no consistent increases in respiratory pathobiont-associated taxa.
Antimicrobial Resistance (ARGs): Baseline nasal ARG abundance decreased following FMT. This reduction was particularly pronounced for genes conferring resistance to $\beta$ -lactams, aminoglycosides, and fluoroquinolones. By Day 56, the nasal resistome profile in the FMT group was comparable to that of healthy controls.

Key Contributions
This work provides empirical evidence that FMT induces systemic changes extending beyond the gastrointestinal tract. The study demonstrates that intestinal microbiota modulation can concurrently alter the microbial ecology and antimicrobial resistance patterns of the upper respiratory tract, specifically the nasal cavity, while leaving the oral cavity relatively unaffected.

Significance
The paper posits that these findings constitute consistent evidence of gut-lung microbial interactions. By linking intestinal dynamics directly with respiratory microbial composition and AMR patterns, the study expands the understanding of the gut-lung axis. It suggests that the systemic impact of gut-targeted therapies like FMT includes measurable modifications to URT communities and their resistance gene profiles, offering a broader perspective on the ecological consequences of microbiome restoration.

Technical Summary: Longitudinal Changes in Nasal and Oral Microbiome and Antimicrobial Resistance Gene Profiles in Response to Human Fecal Microbiota Transplantation

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