Every year, 520,000 children under the age of five die worldwide because of acute gastroenteritis. In fact, although often considered a benign disease, gastroenteritis remains a leading cause of paediatric mortality around the globe. And some bacteria such as Salmonella and Escherichia coli are behind between 10 and 20% of gastroenteritis cases in children.
Now, a new study in mice led by researchers at the University of Michigan Medical School has found that certain bacteria in the gut can protect young mice from infections that ravage their digestive systems.
According to the research, published in Science, a particular bacterium could provide protection against the adverse effects of gastrointestinal infections in newborn mice. This shield-like bacteria were a mixture of Clostridia species. In a series of experiments, scientists saw these played a role not only in helping mice digest the food but also in protecting them from life-threatening infections.
“Any parent knows that new-borns are very susceptible to infections in the first year of life, including enteric, or gut, infections,” says Gabriel Núñez, M.D., the study’s senior author and a University of Michigan pathology professor. “This work suggests that the lack of protective bacteria in the gut microbiota is a mechanism for that susceptibility, perhaps more than the age of the immune system.”
Clostridia is a group of more than 100 species of bacteria inhabiting the gut. According to the research, mice are born naturally without them and start acquiring them a few days later. The days without these protective bacteria make baby mice more vulnerable to infections caused by invading bacteria, which may be similar to how pathogens cause sickness in human babies.
The researchers did an experiment to see how microbes from mice of different ages affected newborn rodents’ vulnerability to infection. They transplanted faecal samples taken from 4- day-old, 12-day-old, 16-day-old, and adult mice into adult germ-free mice; then, they infected those mice with a strain of Salmonella and tracked what happened next with their health.
They saw that half the mice that had received a transplant with the 4-day-old microbes died, whereas all those that got the microbes from adult mice were able to resist the infection.
Then, scientists repeated the experiment with another infectious bacteria, Citrobacter rodentium, similar to the sickness-causing E. coli in humans, and they obtained a similar result as in the previous experiment.
In the next step, scientists transplanted microbes from 4-day-old mice into the germ free animals, but this time they added an extra amount of Clostridia. When they exposed those mice to the pathogenic bacteria, they saw they could resist the infection.
Now researchers are working on further research to find the precise role of Clostridia in offering protection against gut infections and also which strains of this bacterium have a greater effect.
Also, they are investigating how the mother’s milk influences the microbial establishment in newborns and conveys protection from infections. And how, when mice start the weaning process, new microbes from the outside world colonise their guts. Another question they would like to answer is whether there are other species of bacteria that may protect against pathogens, just as Clostridia species do.
The authors think their findings could lead to new approaches for protecting newborns and small babies from these infections affecting their still-immature digestive systems. But further research and experiments in animals are needed before these findings can be tested in humans in a clinical trial.
Yun-Gi K, Kei S, Sang-Uk S, et al. Neonatal acquisition of Clostridia species protects against colonization by bacterial pathogens. Science, 2017. DOI: 10.1126/science.aag2029