COVID-19 and Intestinal Microbiome

The diversity and the quantity of the intestinal microbiome can affect COVID-19 severity as well as the immune system response to infection, according to research published in the journal ¨Gut¨. According to the findings, imbalances in the microbiome composition may also be involved in persistent inflammatory symptoms, the so-called long COVID-19.

COVID-19 is mainly a respiratory disease, but all the current results suggest that the gut may also play an important role. Given the fact that the gut is the largest organ in the body and the microbes it contains affect many immune responses, the researchers wanted to investigate whether the gut microbiome can also affect the immune system response to infection with the new SARS-CoV-2 coronavirus.

Thus, blood and stool samples were taken from 100 laboratory-confirmed patients with COVID-19 infection and from 78 healthy individuals who participated in a microbiome study prior to the onset of the pandemic. The severity of COVID-19 disease was classified as (a) mild, no evidence of pneumonia (b) moderate if there was pneumonia with fever and respiratory symptoms (c) severe if patients had difficulty in breathing normally, and (d) critical if a patient needed mechanical respiratory support or if they developed organ failure requiring an intensive care unit.

To characterize the gut microbiome, the researchers analyzed stool samples from hospitalized patients with COVID-19, and some of them provided stool samples for up to 30 days after they had recovered from SARS-CoV-2 (negative PCR test). Analysis of fecal samples showed that the composition of the intestinal microbiome differed significantly between patients with COVID-19 from the sample of normal individuals, regardless of whether they had been treated with drugs (including antibiotics) or not. Patients with COVID-19 presented higher concentrations of Ruminococcus gnavus, Ruminococcus tors, and Bacteroides dorei in comparison with non-infected individuals. They also had far fewer species that could affect the immune system response, such as Bifidobacterium adolescentis, Faecalibacterium prausnitzii, and Eubacterium rectale. Lower concentrations of F. prausnitzii and Bifidobacterium bifidum were particularly associated with severe infection taking into account antibiotic intake and patient΄s age. Concentrations of these bacteria remained low in samples collected up to 30 days after the recovery.

Infection with the new coronavirus SARS-CoV-2 stimulates the immune system to produce inflammatory cytokines. In some cases, this response may be excessive (cytokine storm), causing extensive tissue damage, septic shock, and multiple organ failure. Blood analysis samples showed that the microbial imbalance observed in patients with COVID-19 could also be associated with elevated levels of inflammatory cytokines and certain markers of tissue damage, such as C-reactive protein (CRP) and various enzymes. This fact suggests, according to the researchers, that the gut microbiome may affect the immune system response to SARS-CoV-2 coronavirus infection and possibly affect the severity and the outcome of the disease.

Some patients who recovered from COVID-19 are known to have persistent symptoms such as fatigue, shortness of breath, and joint pain, sometimes even more than 80 days after the onset of symptoms, and there is evidence to suggest that the dysbiotic gut microbiome could contribute to immune-related problems after recovery from COVID-19.

Enhancing the beneficial bacteria that have been affected during the COVID-19 disease could be a new approach in order to alleviate the serious side effects of the disease, emphasizing the importance of managing the gut microbiome during and after recovery by SARS-CoV-2.

Gianos Stramp

Depicting SARS-CoV-2 fecal viral activity in association with gut microbiota composition in patients with COVID-19, Zuo T, et al. Gut 2021;70:276–284.