Gut microbes may help block infections; however, the mechanisms involved have not been fully identified or understood. Now, studies show that changes in the microbial community after an infection increase the level of a molecule that helps fight harmful bacteria.
Complex interactions between an individual and the intestinal microbiota impact that person’s health and susceptibility to disease. A bit of missing information has been studying the mechanisms that drive those interactions because of the large diversity of species in the microbiota. This diversity is unique to the individual, much like a fingerprint.
Gaining an Understanding of the Mechanisms that Prevent Infection
Scientists are beginning to more fully understand that the gut microbiota has a role in creating resistance to growth of pathogens in the gut. Still, many studies have been descriptive and correlated specific microbiota compositions with a state of disease or health.
Now, a paper published in Cell presents a detailed mechanism by which microbiota fuel the resistance to overgrowth of pathogens.
Scientists generally accept that the gut microbiota can slow the overgrowth of intestinal pathogens. Several lines of evidence support this belief. For instance, high levels or prolonged use of antibiotics may actually enable overgrowth of Clostridium difficile, which causes inflammation of the colon and severe diarrhea. Low diversity of species present in the intestinal microbiota, common in industrialized economies, is linked to a greater susceptibility to infectious diseases. Some studies have shown that mice treated with antibiotics or raised in germ-free environments have greater susceptibility to intestinal pathogens.
Promote or Fight Infection by Pathogens
In other instances, some microbiota may promote growth of or infection by pathogens. For instance, different microbiota in mice determine their susceptibility to a pathogen called Citrobacter rodentium, which leads to an abnormal growth in the colon called hyperplasia.
Microbiota transplantation from susceptible to non-susceptible mice induces susceptibility to C. rodentium infection, whereas microbiota transplantation from non-susceptible to susceptible animals generates resistance to infection.
Epidemiological evidence suggests susceptibility to infections by the food-borne pathogen Campylobacter jejuni depends on the species in the microbiota. This was a study done in Sweden. Other reports show that some pathogens, like Salmonella enterica and C. rodentium, may exploit certain host-microbiota cues to modulate their metabolism and energy creation.
Investigating the Role of Microbiota in Infection
New research is focusing on the role of the microbiota in fighting or inhibiting infection. This research is doing more than documenting relationships between infections and the presence or absence of specific species or combinations of species. It is investigating the mechanisms by which the microbiota provide resistance to infections.
The scientists of this study have shown that after infection with the gut pathogen Klebsiella pneumoniae, mice have a greater ability to resist the bacterium in the future. The researchers analysed microbial DNA, assessing the metagenomes from post-infection microbiota and non-infected microbiota. The objective was to pinpoint how microbes may aid resistance. They found interesting data. The genes that encoded proteins necessary for the metabolism of sulfur-containing molecules were more enriched in post-infection microbiota versus non-infected microbiota.
The researchers reported that infection by a pathogen like Klebsiella pneumoniae in mice impacted gut bacteria. This pathogen can cause an infection due to the enzyme cytochrome oxidase. This enzyme enables the bacteria to generate energy by aerobic respiration using oxygen in the host’s gut. After infection by the pathogen, the level of taurine rises in the intestine. The liver generates taurine through the metabolism of bile acids. The scientists showed that after an infection, the resident bacteria that utilize taurine were more common. When bacteria metabolize taurine, they produce hydrogen sulfide gas, which inhibits aerobic respiration thus blocking the growth of pathogens.
Final Thoughts About Immune Drivers
Intestinal pathogens rely on host-supplied oxygen to create energy through aerobic respiration. This is how they establish their presence and ability to colonize the individual. The study showed a correlation between taurine-mediated production of hydrogen sulfide. This would ultimately inhibit infection by the pathogen.
In addition, they reported that taurine supplements added to the study animals’ drinking water led to similar results. Taurine is a common ingredient in energy drinks, and this discovery of its role in the gut deserves further investigation. A better understanding of such mechanisms could result in targeted manipulation of the microbiota to combat certain infectious diseases.
These results may suggest adding certain dietary supplements like taurine as a way to help the microbiota resist pathogens. This study better identifies the mechanisms by which the microbiota impact respiration, metabolism, and the virulence of intestinal pathogens.