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Wrzburg Chlamydia can apparently survive for a long time in the human intestine. Current experiments using intestinal organoids confirm the hypothesis that chlamydia could persist in this niche. In this way, chlamydia form a permanent reservoir, which carries the risk of reactivation and makes repeated treatment necessary for infected people (PLOS PathogensDOI: 10.1371/journal.ppat.1012144).

Chlamydia is a sexually transmitted infection (STI) that is a globally relevant health problem. The pathogens initially cause no or only mild symptoms, such as itching of the vagina, penis or anus. Chlamydia infections can be successfully treated with antibiotics. If left untreated, serious complications are possible that can lead to infertility or tumors.

After successful antibiotic therapy, some of the previously treated patients return to the clinic with a renewed chlamydia infection. The study authors report that these are often exactly the same strains of bacteria as in the previous infection. Chlamydia can therefore most likely persist in the human body.

Previous experiments on the mouse model indicate that the intestinal tissue represents a natural niche for Chlamydia trachomatis infections and a reservoir for persistent infections. Due to the special properties of the pathogen and the lack of more precise host models, knowledge regarding humans is still limited.

However, it is suspected that the bacteria find a niche in the body in which they are not yet vulnerable, that they form a permanent reservoir there and can become active again later, said Thomas Rudel, head of the Department of Microbiology at the Biocenter of the Julius Maximilian University (JMU) in Würzburg.

The research group then investigated their hypothesis using organoids that were produced in the laboratory from human intestinal epithelial cells. In their experiments, the organoids were successfully infected with chlamydia, for example when the cell epithelium on the intestinal side (apical) was damaged. However, the infections were particularly effective via basolateral cell layers that were facing the bloodstream side.

According to the study authors, the highest infection rates were observed from the bloodstream. In this case, we repeatedly found the persistent forms of the bacteria, which are clearly identifiable under the electron microscope due to their typical shape, explained first author Pargev Hovhannisyan, a scientist at the Institute of Microbiology at the University of Würzburg.

The study authors therefore concluded that chlamydia infection with subsequent persistence would be difficult to spread through the intestines, but could easily occur through the blood. Infected cells sometimes contained both normal and aberrant developmental forms, which indicated cell type-specific reactions during infection. The scientists cite the antigen Pgp3 as an important virulence factor for the infection of human intestinal cells.

Whether their discoveries can be transferred to the human body still needs to be confirmed in clinical studies, Rudel said. His research group next wants to investigate whether chlamydia prefer certain cell types in the intestine for their persistence stages.

After all, the intestine consists of hundreds of different types of cells, say the authors. However, they admit that it could also be that other factors from the surrounding tissue promote persistence mechanisms.

The study authors cite the lack of natural microbiota and a functioning innate and adaptive immune system as limitations of their organoid model. The authors also point out that intestinal microbiota and the immune system are important factors that protect the intestinal epithelium from pathogens. © cw/aerzteblatt.de