Bacteria such as Yersinia enterocolitica and Yersinia pseudotuberculosis cause thousands of gastrointestinal infections each year in Germany alone. The bugs usually enter the human body via contaminated foods, for example raw pork meat. An infection can elicit severe diarrhoeal diseases or vomiting. This is the body's way to eject the majority of the pathogens – and the immune system takes over the remaining clean-up work.
In most cases, an infected organism manages to eliminate the bacteria completely. However, some Yersinia infections become chronic, which can then promote autoimmune diseases such as reactive arthritis. A research team led by Prof Petra Dersch now wanted to find out how the bacteria manage to survive for years inside the body without being detected by the immune system of the host.
To study how a living organism fights off the infection, the scientists infected mice with the bugs. The animals usually overcome a Yersinia infection rapidly, but approximately ten percent of the mice succumb to the disease and another ten percent maintain a chronic infection. The team analysed the gene activity of the bacteria in acutely and chronically infected animals. "We found the production of CNFY in the persisting, i.e. surviving, yersiniae to be down-regulated," says Petra Dersch.
CNFY is a toxin that some Yersinia strains produce during the acute infection phase. In the host cells, the substance blocks cell division which, in turn, leads to a steadily increasing cell size and facilitates the attack by the pathogen. "Yersinia uses CNFY to accelerate the spread of the infection and inflammation in the tissue, which is ultimately fatal for the infected host," says Prof Petra Dersch, "but in the absence of CNFY, the immune system no longer detects the bacteria, and the mice survive. This trick allows the yersiniae to hide for months in the guts of the animals."
Microscopic analysis also revealed a difference between bugs that were causing acute versus chronic infection: During acute infection phases, the rapidly growing bacteria formed micro-colonies. In contrast, the persistent bacteria were found as single cells within the tissue, which makes them more difficult to detect by the immune system.
(© Andreas Fischer / HZI / AcademiaNet)