The bacterium Chlamydia trachomatis is best known for infecting genitals, causing the sexually transmitted infection (STI) known as chlamydia. But a new study has found that these sneaky cells can also infiltrate our guts, building a hidden supply of bacteria that could then leak to the genitals and cause reoccurring infections.
The findings could ultimately change the type and duration of antibiotic treatment used to neutralize the infection, according to researchers.
Chlamydia is one of the most common STIs in the world, with the World Health Organization estimating that 129 million people contracted the bacteria in 2020. Though curable with antibiotics and usually mild, the disease can cause pelvic inflammation, infertility by blocking the fallopian tubes and even life-threatening ectopic pregnancies.
Most often thought of as a genital infection, indirect evidence has been steadily building that the bacteria may be able to infect our guts. Other Chlamydia species are known to infect the intestinal tracts of wild and domestic animals, and, in a 2016 study, mice injected with mouse-specific Chlamydia developed infections in their guts.
These results led Patrik Bavoil, Ph.D., a microbiologist at the University of Maryland, and colleagues to hypothesize that the human Chlamydia, called C. trachomatis, originally evolved to live in our gastrointestinal system without causing harm.
The latest research by Thomas Rudel, Ph.D., a microbiologist at the University of Würzburg in Germany, has continued to explore this possibility.
“While studying [C. trachomatis] infection in human primary epithelial cells derived from the female genital tract, we came up with the idea of modeling the infection in the human gut tissue,” Rudel told Fierce in an email. “We were intrigued by the fact that for many of the other closely related chlamydial species, which naturally infect different animals, the infection often localized to the GI tract and was of persistent nature.”
To see what chlamydia might be doing in our guts, Rudel’s team grew healthy gastrointestinal tissue taken from patients at the university hospital into mini-organs. They then infected the organoids with a strain of C. trachomatis that glows, allowing them to see that the bacteria did infiltrate the cells.
The researchers then grew the cultured cells into thin layers, just one cell thick, that enabled them to see how the bacteria were getting into the cells.
The results, published in PLOS Pathogens on Aug. 22, “establish that the infection occurs only from the basolateral side,” Bavoil told Fierce, meaning the edges of the cells that are normally in contact with other cells rather than from the side of the cell that faces the gut cavity.
How the bacteria are reaching the “back door” of cells and infecting them needs more study, Rudel said. It could be that tiny cuts, inflammation or cancer could provide openings for the bacteria to slink through, he said, or it could possibly reach cells through the bloodstream.
Once successfully settled in the gastrointestinal tract, Chlamydia cells can make their way to the genitals and become a source of persistent reinfection. This could happen due to the close proximity of the gut’s endpoint, the anus, and the genitals, but traveling through the bloodstream is again a possibility.
Though there are many open questions, both Rudel and Bavoil believe it’s time to rethink our understanding of our common bacterial foe—and how we treat it.
“We think that more attention should be paid to the possibility that during the regular treatment of genital infections, especially in patients with recurrent infections, Chlamydia might not be completely eliminated from the body,” Rudel said. “Due to the varying susceptibility of the different anatomical regions to antibiotics, this could also have implications for the choice and the duration of the antibiotic therapy.”
Bavoil, who wasn't involved in the study, also sees big implications for the research.
“Chlamydia’s status going from that of an established genital, strictly sexually transmitted pathogen to that of an innocuous gut microbe that gets naughty when it gets out of its home would be a paradigm shift of some proportion,” he said.