The teeming hordes of bacteria that live in our gastrointestinal tracts – about 3 pounds’ worth by the latest count -- are still something of a mystery. Some help us break down food, while many others are just hitching a ride. But some are either actively working against us, or thrive only when we’re sick.

Now a new study is looking at a possible link between pathogenic gut bacteria and diabetes.

An international team of researchers has found that having more hostile bacteria living in your gut was a reliable flag indicating whether or not a person has type 2 diabetes.

The researchers examined the intestinal bacterial landscapes of 345 Chinese volunteers, 171 of whom had type 2 diabetes. They published their findings in the journal Nature on Wednesday.

The diabetes patients all had characteristic similarities in the composition of their gut bacteria: “a moderate degree of gut microbial dysbiosis” --  basically, an imbalance in gut bacteria – decreased abundance of some butyrate-producing bacteria, which are thought to help maintain health in the colon, and an increase in various opportunistic pathogens, according to the paper.

"It is important to point out that our discovery demonstrates a correlation,” co-author Karsten Kristiansen said in a statement Wednesday. “The big question now is whether the changes in gut bacteria can affect the development of type 2 diabetes or whether the changes simply reflect that the person is suffering from type 2 diabetes."

The results confirm previous studies in Denmark, which also found that diabetes sufferers had imbalances in intestinal bacteria.

Other researchers have found that certain gut bacteria can overcome genetic protections against diabetes. A 2011 research paper published in the journal PLoS Biology described how genetically engineered mice that should have been insulin-sensitive developed insulin resistance after their gut microbial composition changed. Further investigation showed a possible link between a component of bacterial cell membranes, a class of compounds called lipopolysaccharides, and insulin resistance.

Next, scientists hope to establish whether or not people at risk for developing diabetes already have distinctive microbial communities, and investigate whether the bacteria play a direct role in the development of the condition.

"We are going to transplant gut bacteria from people that suffer from type 2 diabetes into mice and examine whether the mice then develop diabetes," Oluf Borbye Pedersen, a University of Copenhagen researcher and co-author of the Nature paper, said in a statement on Wednesday.

Knowing how gut bacteria influence disease could be an important step in treating it. In April, scientists managed to reverse type 1 diabetes in lab mice by administering bacteria specially designed to counter an immune system overreaction to insulin-producing cells.

SOURCE: Qin et al. “A metagenome-wide association study of gut microbiota in type 2 diabetes.” Nature published online 26 September 2012.