Covid-19: How the virus changes the intestinal flora

Is there a connection between the course of infectious diseases such as Covid-19 and the composition of the intestinal flora?

Scientists working with Jonas Schlueter and Ken Cadwell from New York University in New York City have asked themselves these questions.

In a first step, they tested mice to see how infection with SARS-CoV-2 affects the intestinal flora.

The results, currently in

the peer review process of

a

Journal, were recently published in the preprint journal

submitted. As can be seen from this work, which has not yet been assessed, the microbial diversity in the intestines of the infected animals decreased noticeably. Some types of bacteria multiplied excessively, while the number of others fell sharply. The imbalance of the intestinal flora was particularly pronounced in rodents infected with large amounts of virus. These animals looked much sicker than those that had only had contact with low numbers of viruses.

In a next step, the scientists investigated the question of whether comparable processes take place in humans. To do this, they examined the stool samples from 138 men and women who had been hospitalized for an infection with SARS-CoV-2. The result: In the case of Covid-19 patients, the diversity of the intestinal microbiome was also reduced, and that even more sustainably than in the rodents. In some patients, more than half of the intestinal flora consisted of just one single bacterial species. As in the case of the mice, there was a sharp decrease in the types of bacteria that are believed to support the immune system. However, the loss of microbial diversity did not affect all infected people equally.It was particularly pronounced in the intensive care patients and especially in the 21 patients who suffered from bacterial sepsis ("blood poisoning").

Types of intestinal bacteria promote the immune system

Further analyzes then revealed striking similarities between the microbial population in the intestine and the pathogens in the blood. The blood invaders were the same bacteria that had spread in the intestines at the expense of other families of microbes. The authors of the study therefore consider it obvious that the blood poisoning originates from the digestive tract. As a result of the virus attacks or the violent inflammatory reactions, they suspect, the intestinal wall could become permeable and open the door to invasive bacteria in this way. As they add, the usually overly generous use of antibiotics for corona patients also harbors dangers. For example, 80 percent of the sepsis patients in their study had already received such drugs before the onset of blood poisoning.This could also have harmed those affected. Because it is well known that antibiotics reduce the diversity of microbes in the intestine and thus promote the spread of therapy-resistant germs, the breeding ground for sepsis.

Interesting in this context are the

results of a previous study by Schlueter at the Memorial Sloan Kettering Cancer Center in New York City,

recently published in the journal

. As these suggest, certain types of intestinal bacteria - including those that were present in severely reduced numbers in seriously ill corona patients - promote the multiplication of white blood cells and therefore possibly strengthen the physical defense. The participants in the study, around a thousand people with advanced leukemia, provided the conditions to shed light on the connection between the intestinal flora and the immune system.

Because the immune cells of those affected were destroyed with high-dose chemotherapy and then rebuilt with a stem cell transplant. This made it possible to follow the recovery of the immune system day by day and to relate each to the intestinal microbiome. In future studies, the scientists now want to find out whether and how these findings can be used therapeutically.