In the Lab, Stress Harms Gut Bacteria Unbeknownst to most individuals, 90 trillion bacteria reside in the human digestive tract. The bacteria help the immune system stay on track and alert for infections.

New research suggests stress can harm the good bacteria and overstimulate the human immune system. However, the exact mechanism by which stress interferes with the bacteria has yet to be determined.

In new research, Michael Bailey, Ph.D., attempted to discover how stress changes these bacteria and if there was any sort of biological function associated with effects on these bacteria.

Bailey and colleagues used mice to learn how bacteria help to maintain a balanced immune system. In a series of experiments, researchers subjected one group of mice to stress by placing an aggressive mouse in a cage of more docile mice.

They then compared biomarkers from blood samples taken from the stressed mice to a control group.

Compared to the control mice, the stressed animals showed two marked differences: The proportion of one important type of bacteria in the gut (Bacteroides) fell by 20 to 25 percent while another type (Clostridium) increased a similar amount.

Also, levels of the two biomarkers jumped tenfold in the stressed mice, compared to controls.

The researchers then treated stressed mice with broad-spectrum antibiotics that could kill as much as 90 percent of the intestinal bacteria for a short period.

When they again looked at the two immune biomarkers in the stressed mice, they saw the biomarkers had increased by only one-fifth as much.

Consequently, the experiments show that bacteria are involved in the ability of stress to prime the innate immune system.

According to the researchers, the next goal is to better understand the roles that the bacteria play in activating the immune system, and to determine if other factors are playing a key role in the process.

Source: Ohio State University