STD Awareness: Three Sexually Transmitted Bacteria That Will Shock and Amaze You

It’s hard to appreciate a pubic louse as an intriguing creature in its own right. Not when an infestation with pubic lice is such a vexing experience. The same can be said for the germs that cause any number of human diseases. But, just as you might have marveled at the microorganisms you spied under the microscope in your high school biology class, the bacteria and other microbes that cause sexually transmitted diseases (STDs) can be fascinating, strictly as scientific subjects.

Let’s look at a few of these fascinating bacteria!

Treponema pallidum, the causative agent of syphilis, is seen in this electron micrograph adhering to a surface with the tapered end of its structure. Image obtained from the CDC’s Public Health Image Library.

Image: Public Health Image Library, CDC

Treponema pallidum: the bacteria that cause syphilis

Before the age of antibiotics, syphilis was the most feared STD out there. Untreated, it can cause serious, sometimes fatal, damage to the body, and can also spread to a fetus during pregnancy. But did you know that earlier versions of syphilis might have been even worse?

Written records of syphilis date back to 1495 when it seemed to appear in Europe for the first time. According to a 1519 description, it caused

Boils that stood out like Acorns, from whence issued such filthy stinking Matter, that whosoever came within the Scent, believed himself infected. The Colour of these was of a dark Green and the very Aspect as shocking as the pain itself, which yet was as if the Sick had laid upon a fire.

Interestingly, such descriptions don’t match modern forms of syphilis, which suggests that it might have evolved into a less virulent form, possibly in response to selective pressure against symptoms that render the host sexually unappealing. Basically, that means that someone with boils emitting “filthy stinking Matter” might have trouble find sexual partners; the pustules of yore don’t seem to decorate the epidermis of contemporary sufferers, making them more likely to perpetuate milder forms of syphilis through sexual transmission.

We can’t hop into a time machine and take samples from European syphilitics in 1495, but some biologists believe that it took about 50 years for evolution to work its mojo on the disease, giving rise to the milder Syphilis 2.0 in the mid-1500s. Continue reading

STD Awareness: Chlamydia trachomatis

A colony of C. trachomatis (colored green) is nestled inside a human cell. Image: V. Brinkmann, Max Planck Institute for Infection Biology

A colony of C. trachomatis (colored green) is nestled inside a human cell. Image: V. Brinkmann, Max Planck Institute for Infection Biology

In the microscopic world of germs, organisms called Chlamydiae are dwarfed by their fellow bacteria. An E. coli bacterium can hang out with 100,000 of its closest friends on the head of a pin, but Chlamydiae are smaller still. Infectious particles are about one-tenth the length of an E. coli, rivaling the size of a large virus. And, just like a virus, Chlamydiae can still pack quite a punch, proving that sometimes, not-so-good things can come in small packages.

There are many types of Chlamydiae bacteria, but one species, Chlamydia trachomatis, is responsible for not one, but two sexually transmitted diseases (STDs) in humans: chlamydia and lymphogranuloma venereum (LGV). (Humans aren’t the only ones affected by sexually transmitted Chlamydiae. A different species, Chlamydia pecorum, is devastating wild koalas in Australia, which has got to be one of the biggest bummers ever.)


Chlamydia is a case study for the importance of safer sex and regular STD testing.


Chlamydia is one of the most common STDs in the United States — there were almost 1.5 million diagnoses in 2011 alone, but experts estimate that there were around another 1.5 million cases of chlamydia that went undiagnosed. How can this be? Chlamydia is often a “silent” infection, meaning that symptoms are rare, allowing people to harbor these bacteria without even knowing it. (When symptoms do occur, they might include swelling in the genital region; vaginal, cervical, or penile discharge; or painful urination.)

It might seem like a small mercy that this common infection is unlikely to torture us with harrowing symptoms — but, in actuality, those of us who have to deal with discharge or burning urination should try to appreciate the heads up: Left untreated, chlamydia can cause serious complications. When it spreads along the female reproductive tract, it can cause pelvic inflammatory disease, which can severely compromise fertility and cause chronic pain. Rarely, in a male reproductive tract, it can cause epididymitis, which can also spell bad news for future fertility. Continue reading