Cases of bacterial sexually transmitted infections are on the rise worldwide. An international team led by the University of Zurich has now developed a new method for genome sequencing and discovered a previously unrecognized strain of chlamydia.

According to the World Health Organization (WHO), hundreds of millions of new cases of bacterial sexually transmitted infections (STIs) are reported worldwide each year. Many infections go undiagnosed due to their often silent symptoms, contributing to transmission, disease and complications such as infertility and miscarriage. Tackling the global STI challenge of bacteria that cause chlamydia, gonorrhea, syphilis and also Mycoplasma genitalium remains a significant public health concern. With rising infection rates and increasing antimicrobial resistance, understanding these pathogens is vital for improving diagnosis, treatment and prevention strategies.

The challenge of understanding STIs
Studying the bacteria behind STIs is notoriously difficult. Many of these pathogens cannot be grown in laboratories, and clinical samples contain overwhelming amounts of human DNA, making genome sequencing of bacterial STIs a daunting task. However, the genome contains the genetic information of these bacteria, including how related they are to each other, and how resistant they are to antibiotics.

A team of scientists led by Helena Seth-Smith from the University of Zurich (UZH), Switzerland, with international collaborations to the University of Buenos Aires, Argentina, has developed a cutting-edge “target enrichment” technology. Using specially designed molecular probes, they “fished” for bacterial STI DNA from clinical samples, enabling high-resolution genome analysis. “This method helps us to understand how Chlamydia spreads and adapts,” says Helena Seth-Smith, co-head of microbial genomics and head of bioinformatics at the Institute of Medical Microbiology.

Discovery of a new chlamydia lineage
The team discovered a previously unknown lineage of Chlamydia trachomatis in Argentina. This novel strain “ompA-genotype L4”, which has different genetic characteristics from the three known strains, was found in rectal samples from men, who have sex with men. Chlamydia is mainly transmitted through the mucous membranes during unprotected sex. The patients with lineage L4 typically showed symptoms such as rectal inflammation, difficult or urgent bowel movements and rectal discharge.

“Our findings open a new frontier in understanding STIs and emphasize the dynamic nature of STI transmission and development pathways,” said Karina Büttner from UZH. “With these tools, we can better support public health efforts to control and prevent these infections.”

A path forward
Global cooperation in tracking these infections is essential. Sexually transmitted diseases often affect population groups with little or no access to health care or education. According to the researchers, the new methods and a better understanding of the genetic makeup of the pathogens will make it possible to identify trends in antibiotic resistance, improve diagnostic tests and tailor treatments to the growing threat posed by STIs.