Public release date: 1-Sep-2013 [ | E-mail | Share ]

Contact: Bruce Goldman goldmanb@stanford.edu 650-725-2106 Stanford University Medical Center

STANFORD, Calif. A new study by researchers at the Stanford University School of Medicine could help pinpoint ways to counter the effects of the antibiotics-driven depletion of friendly, gut-dwelling bacteria.

A number of intestinal pathogens can cause problems after antibiotic administration, said Justin Sonnenburg, PhD, assistant professor of microbiology and immunology and the senior author of the study, to be published online Sept. 1 in Nature. Graduate students Katharine Ng and Jessica Ferreyra shared lead authorship.

"Antibiotics open the door for these pathogens to take hold. But how, exactly, that occurs hasn't been well understood," Sonnenburg said.

In the first 24 hours after administration of oral antibiotics, a spike in carbohydrate availability takes place in the gut, the study says. This transient nutrient surplus, combined with the reduction of friendly gut-dwelling bacteria due to antibiotics, permits at least two potentially deadly pathogens to get a toehold in that otherwise more forbidding environment.

In the past decade or so, much has been learned about the complex microbial ecosystem that resides in every healthy mammal's large intestine, including ours. The thousands of distinct bacterial strains that normally inhabit this challenging but nutrient-rich niche have adapted to it so well that we have difficulty living without them. They manufacture vitamins, provide critical training to our immune systems and even guide the development of our own tissues. Antibiotics decimate this gut-microbe ecosystem, which begins bouncing back within a few days but may take a month or more to regain its former numbers. And the ecosystem appears to suffer the permanent loss of some of its constituent bacterial strains.

It is thought that our commensal, or friendly, bacteria serve as a kind of lawn that, in commandeering the rich fertilizer that courses through our gut, outcompetes the less-well-behaved pathogenic "weeds." It has also been suggested that our commensal bugs secrete pathogen-killing factors. Another theory holds that the disruption of our inner microbial ecosystem somehow impairs our immune responsiveness.

"While these hypotheses are by no means mutually exclusive, our work specifically supports the suggestion that our resident microbes hold pathogens at bay by competing for nutrients," Sonnenburg said.

When that defense falters, as it does shortly after a course of antibiotics begins, marauding micro-organisms such as salmonella or Clostridium difficile can establish beachheads. Once they reach sufficient numbers, these two parasitic invaders can mount intentional campaigns to induce inflammation, a condition that impairs the restoration of our normal gut ecosystem but in which salmonella and C. difficile have learned to prosper.

Excerpt from:
Stanford scientists show how antibiotics enable pathogenic gut infections