Method developed to culture bacteria that causes syphilis

June 26 (UPI) -- Researchers have developed a way to culture the elusive bacteria that causes syphilis.

Despite a century of work, scientists haven't been able grow the spiral-shaped bacterium, called Treponema pallidum.

But researchers at the University of Texas Health Science Center at Houston developed a new method in which the spirochetes are grown in rabbit epithelial cells and fed periodically with amino acids.

They published their findings Tuesday in the journal mBio.

Researchers hope their work someday will lead to new ways to detect, treat or prevent the infection. If diagnosed early, the disease is easy to treat.

The bacteria is transmitted sexually, via blood transfusion or from mother to child.

In 1998, the Centers for Disease Control and Prevention launched a syphilis eradication effort. But primary and secondary syphilis have grown over the last two decades. In 1994, there were 2.1 cases per 100,000 compared with 7.5 per 100,000 in 2015, according to the CDC.

Researchers haven't been able to culture the bacteria because it is dependent on its human host.

"The organism never touches the ground," senior author Dr. Steven Norris, a microbiologist in the biomedical sciences at McGovern Medical School in House, said in a press release by the American Society for Microbiology. "It's only found in humans. It's not found anywhere else in nature."

Previously, researchers injected rabbits with bacteria from a human and waited a few weeks to confirm an infection.

"It was a very inefficient process," Norris said.

They modified a version first introduced in 1981 that kept the bacteria alive for about 18 days.

The researchers' complex culture medium, which is often used to culture Lyme disease, mimics the environment where the bacteria are found naturally.

They transfered the infected cells to a new culture medium about once a week. Then they used an electron microscopy to verify that the structure of the bacterium remained unchanged during culture.

"We expected they would grow a little faster than they do, but maybe they're just slow-growing organisms," study leader Dr. Diane Edmondson, an assistant professor of pathology and laboratory medicine at UTHealth, said. "One of the reasons for success is accepting that we're never going to get 1010 organisms per milliliter. We work with what it really is."

They hope to used the method to culture spirochetes that cause syphilis-related diseases including yaws and bejel, which are spread by body contact.