Biologists describe syphilis agent to help develop a vaccine

Syphilis has been plaguing humanity for over five hundred years and in recent decades there has been no success in bringing the numbers of new cases down. The infection also causes serious foetal damage in pregnant women, who account for at least a million of the ten million new cases every year. Researchers are therefore trying to map the genome of the bacteria that causes the disease.

David Šmajs from Masaryk University has been studying Treponema pallidum, the syphilis agent, for a number of years. Together with his team, he recently participated in an extensive study of the bacteria’s genome. Thanks to this research, which was published in Nature Microbiology, an international group of scientists was able to discover a group of strains that are resistant to some antibiotics.

According to the results of the study, the currently dominant agents of the disease are part of a group that only arose after the introduction of antibiotics. These strains are now dominant in most of the developed world.

 “We found that most of the bacteria that cause syphilis are genetically very similar to one another. However, this particular large group is also resistant to azithromycin, which can be used in some people to treat syphilis or related diseases instead of the traditional penicillin treatment,” says Šmajs, who is an employee of the Department of Biology at the MU Faculty of Medicine. These resistant strains of the syphilis agent are usually found in big cities.

A smaller portion of the strains is genetically different and more varied. These strains are sensitive to both antibiotics and are mostly found in areas further away from Europe, such as Argentina, northern Canada or Madagascar.

Stealth pathogen
Šmajs adds that understanding the genetic variability of the bacteria causing syphilis can help in developing a vaccine against the disease. “All efforts in this area have so far been unsuccessful, because the agent that causes the disease is unusually skilful in avoiding the human immune system. This is why the Treponema pallidum bacteria are sometimes called stealth pathogens.

Understanding the genetic variability of syphilis agents can help find places that could be the key for their recognition by the immune system. This could help develop a vaccine and thereby also stop the spread of this sexually transmitted disease.

The study, conducted with the participation of four experts from the Faculty of Medicine, was groundbreaking in another way as well. The researchers worked with scores of samples taken from patients. This was the first time that the whole syphilis genome was studied in samples collected from patients. This is a relatively difficult process, as these samples only contain a very small amount of the bacterial DNA.

As Šmajs notes, “Moreover, T. pallidum cannot be cultivated in a culture medium, so it had to be multiplied in laboratory animals first, before any research could take place. One of the findings of the research is also the fact that this method is no longer necessary, thanks to new techniques available to us.”

Research into the syphilis agent continues in Brno as well as within the international research consortium. Researchers are now turning their attention to the typology of the bacterial strains that are present in human beings. Thanks to the newly gained understanding of the differences between the individual strains, it is now possible to create an overview based solely on the differences in selected places of the genome.

Researchers are also interested in the evolution of T. pallidum. “Our goal is to determine, through further study of the genetic information, when the agents divided into separate strains,” Šmajs says. “In the case of modern strains, which were the object of our study, we found a common ancestor from after the discovery of the Americas. However, it is possible that it could have happened much earlier.” He adds, “We would also like to discover when and how syphilis first appeared.”

Masaryk university