Gastrointestinal symptoms of long COVID-19 related to the ectopic colonization of specific bacteria that move between the upper and lower alimentary tract and alterations in serum metabolitesOriginal paper
Karen Pendergrass is a microbiome researcher specializing in microbiome-targeted interventions (MBTIs). She systematically analyzes scientific literature to identify microbial patterns, develop hypotheses, and validate interventions. As the founder of the Microbiome Signatures Database, she bridges microbiome research with clinical practice. In 2012, based on her own investigative research, she became the first documented case of FMT for Celiac Disease, four years before the first published case study.
Read MoreWhat was studied?
This study examined how the oral and gut microbiomes and serum metabolites change in patients with gastrointestinal symptoms of long COVID-19. It focused on mild cases from a 2022 outbreak. Fecal samples underwent shotgun metagenomic sequencing, and saliva underwent species-level 2bRAD-M sequencing. Paired serum samples were profiled by widely targeted metabolomics. Two published gut microbiome cohorts were reanalyzed for comparison.
Who was studied?
Researchers prospectively enrolled 983 antibiotic-naive hospitalized patients with mild COVID-19 in Shanghai, China, and followed them for 3 months after discharge. At follow-up, 45 patients had gastrointestinal long-COVID symptoms (about 4.6%); 8 patients without such symptoms and 25 healthy controls were also sampled. Paired saliva and fecal samples came from all 45 long-COVID patients, plus 33 serum samples. None had prior GI disorders or used probiotics or antibiotics.
What were the most important findings?
Long-COVID patients showed significantly reduced gut alpha diversity at follow-up (Chao1, Shannon, Simpson all p less than 0.0001) with widespread depletion of gut taxa. Oral bacterial abundance, by contrast, increased. Proteobacteria was the only shared differential phylum. 27 Proteobacteria genera moved in opposite directions between gut and mouth, suggesting ectopic oral colonization by gut microbes led by Neisseria, Lautropia, and Agrobacterium. Oral Neisseria and Lautropia correlated strongly with potentially toxic serum metabolites such as 4-chlorophenylacetic acid, 5-sulfoxymethylfurfural, and estradiol valerate.
What are the greatest implications of this study?
The results propose a mechanism for GI long-COVID: gut Proteobacteria ectopically colonize the oral cavity and link to harmful shifts in serum metabolites. This highlights the oral-gut microbiome axis. Mild patients without long-COVID showed little microbiome change, suggesting these shifts are specific to symptomatic patients. The authors stress this ectopic colonization concept needs validation with tissue sampling. Follow-up relied on telephone contact, a noted limitation. Causation is not established.