Gut Bacteria That Battles Salmonella Infection

Salmonella are rod-shaped bacteria that can cause gastrointestinal infections (gastroenteritis) in humans and many animals. Especially with members of risk groups such as infants, small children, elderly or immunocompromised people, a salmonella infection can be difficult. In contrast, people with an intact intestinal flora are usually protected. Only about 10 to 20 percent of those who ingest the germs - usually on contaminated food - it comes to an infection at all. Which bacteria in the intestinal flora but possibly the cause of the protective effects, is so far largely unknown. Scientists around Bärbel Stecher, A professor at the Max von Pettenkofer Institute of the LMU and member of the German Center for Infection Research (DZIF), has now succeeded in identifying a bacterium that is resistant to infections with Salmonella enterica serovar Typhimurium in the mouse model - one of the two most common subspecies in Germany. protects. The researchers report on their findings in the journal Cell Host & Microbe .

The gut of healthy humans and mice is densely populated with bacteria and other microorganisms. This natural intestinal flora can protect against infections with Salmonella, because in particular the commensal bacteria produce inhibitors there, occupy all niches and consume relevant nutrients such as sugar or proteins, but also oxygen. Sandrine Brugiroux and Debora Garzetti from the research team compared the microbiome of various mouse groups to investigate how a healthy intestinal flora is assembled that optimally protects against infections. The animals of one group had been shown to be protected against Salmonella infections, the mice of the other groups not.

The scientists found that in the protected mice bacteria of the species Mucispirillum schaedleri occur, in the other group, these are missing. M. schaedleri belongs to a large group of bacteria whose representatives live mainly in mud or sediments - only Mucispirillum occurs in the intestine of warm-blooded animals, in mice like humans. "So far, it has been thought that this bacterium is not so common in humans," says Stecher, "but in stool examinations, M. schaedleri is often not detected, as these bacteria accumulate in the mucus layer of the intestine. In studies in which the intestinal mucosa was examined, the bacteria were found in 50 percent of the subjects.

In a next step, Simone Herp, who has just completed her doctoral thesis at the Max von Pettenkofer Institute, introduced a so-called gnotobiotic model. These are mice whose intestines are initially germ-free and can be colonized in a targeted manner, so that they carry a defined intestinal flora. "We generated a group of mice that have mucispirillum in their intestines and another without these bacteria. We have experimentally infected both groups with salmonella and have actually shown that mucispirillum is causally associated with protection against Salmonella infections, "says Stecher.

Further investigations by the researchers showed that the protective effect of Mucispirillum is based on the fact that the bacteria compete with Salmonella for certain nutrients, for example nitrate. Although Salmonella does not necessarily grow slower due to this competition, it can no longer produce its most important virulence factor - the property on which the pathogenic effect is based. This virulence factor, a so-called type III secretion system, acts as a kind of molecular needle that injects Salmonella toxins into the epithelial cells. As a result, they can penetrate into the epithelial cells and it ultimately comes to inflammation and gastroenteritis.

The results of the scientists may possibly lead to the development of new prevention methods in the long term. "But until then much research is needed," emphasizes Stecher, "we still do not know, for example, whether and which other - possibly negative - effects M. schaedleri has in the gut." 

This article has been republished from materials provided by Ludwig-Maximilians-Universität München. Note: material may have been edited for length and content. For further information, please contact the cited source.

Reference
Simone Herp, Sandrine Brugiroux, Debora Garzetti, Diana Ring, Lara M. Jochum, Markus Beutler, Claudia Eberl, Saib Hussain, Steffi Walter, Roman G. Gerlach, Hans J. Ruscheweyh, Daniel Huson, Mikael E. Sellin, Emma Slack, Buck Hanson, Alexander Loy, John F. Baines, Philipp Rausch, Marijana Basic, André Bleich, David Berry, Bärbel Stecher. Mucispirillum schaedleri Antagonizes Salmonella Virulence to Protect Mice against Colitis. Cell Host & Microbe, 2019; DOI: 10.1016/j.chom.2019.03.004.