Page 25 - Read Online

Page 2 of 10 Xiao et al. Microbiome Res Rep 2024;3:7 https://dx.doi.org/10.20517/mrr.2023.48

INTRODUCTION
The human gut microbiota plays a crucial role in maintaining our overall health, as it helps in digestion,
[1]
absorption of nutrients, and the development of our immune system . Any alteration in the gut microbiota
can lead to various health problems, including inflammatory bowel disease, obesity, diabetes, and even
mental disorders. This imbalance, known as gut microbiota dysbiosis, can be instigated by a variety of
[2]
factors such as diet, age, medication, and infections . Recent studies have shown that viral respiratory
[3]
infections can cause gut microbiota dysbiosis by altering the microbial composition of the gut . Conversely,
changes in the gut microbiota can even affect the disease outcomes of distant organs, including the lung,
which has been demonstrated by transfer experiments with dysbiosis of the gut microbiota .
[4]
Corona Virus Disease 2019 (COVID-19) is an infectious disease first recognized in Wuhan, China, in
December 2019 . The pandemic of COVID-19 was a global public health emergency caused by the
[5]
widespread infection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the
development of infectious respiratory diseases. While respiratory symptoms dominate the clinical
syndromes of COVID-19 cases, a subset of patients grapple with concurrent gastrointestinal manifestations
such as diarrhea and nausea. Individuals afflicted by COVID-19 manifest discernible alterations in gut
microbiota. Upon hospitalization, their gut microbiota demonstrates an enrichment of opportunistic
pathogens, coupled with a decline in beneficial commensals .
[6]

This review explores the gut microbiota dysbiosis observed in patients who are infected with COVID-19
and plausible mechanisms culminating in this dysbiosis, unraveling the interplay of factors that orchestrate
the microbial imbalance. Furthermore, it delves into the aftermath of COVID-19-induced gut microbiota
dysbiosis, spotlighting its pivotal role in heightening the risk of systemic maladies. Overall, by shining a
spotlight on the relationship between COVID-19 and gut microbiota, this review accentuates the imperative
of comprehending its impact on human health and offers a stepping stone for potential interventions and
safeguards.

GUT MICROBIOTA ALTERATIONS IN PATIENTS INFECTED BY COVID-19
The gut microbiota is the densest bacterial community known to exist in the human body and plays an
important metabolic and immune process in human health by metabolizing indigestible carbohydrates,
producing vitamins, preventing pathogen infections, and modulating host immune responses . Since the
[7]
outbreak of COVID-19, extensive research has been conducted on its various symptoms and impacts. In
addition to the main respiratory symptoms, more and more studies have shown that COVID-19 also affects
the composition and function of human gut microbiota .
[8,9]
Zuo et al.’s pioneering study revealed the disruption of gut microbiota in COVID-19 patients, highlighting
stark differences in fecal microbial composition compared to healthy counterparts. Hospitalized COVID-19
patients exhibited an enrichment of bacteremia-associated microbial communities, accompanied by a
decline in commensals beneficial to host immunity. The baseline abundances of Coprobacillus, Clostridium
ramosum, and Clostridium hathewayi were positively correlated with the severity of COVID-19, while
Faecalibacterium prausnitzii was negatively correlated with severity . In another parallel study, Zuo et al.
[6]
reported that fecal fungi of COVID-19 patients showed greater individual differences compared with
healthy individuals, revealing higher heterogeneity. Compared with healthy individuals, patients infected by
COVID-19 had increased proportions of opportunistic fungal pathogens, Candida albicans, Candida auris,
and Aspergillus flavus . Interestingly, COVID-19’s influence on gut microbiota is intertwined with changes
[10]
in oral and respiratory microbiota. Some similarities were found in the changing patterns of the
composition of respiratory, oral, and gut microbiota, but whether these patterns result from microbial