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.

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

Image: V. Brinkmann, Max Planck Institute for Infection Biology

Chlamydia trachomatis: the bacteria that cause chlamydia

In the microscopic world of germs, organisms called Chlamydiae are dwarfed by their fellow bacteria. Infectious particles are about as tiny and simplified as a life form can be and still be considered living. But don’t be fooled by their diminutive stature: Infection with Chlamydia trachomatis is the most common reported infection in the country! It usually has no symptoms, and, untreated, chlamydia can lead to infertility in both males and females.

Sadly, humans aren’t the only ones affected by sexually transmitted Chlamydiae. Chlamydia pecorum is devastating wild koalas in Australia. Chlamydia has reached epidemic proportions among koalas, and some populations have an infection rate of 90 percent! Koalas are currently considered a threatened species, and some worry that they are at risk for extinction — not only in the face of chlamydia, but also as a result of urban development, as koalas are pushed off their land or struck by cars.

Because koalas can’t be taught to use condoms — unlike humans! — Australian scientists are working hard to produce a vaccine that will protect them from chlamydia. And, who knows, that vaccine might provide a basis for a human version!

Image: National Institute of Biomedical Imaging and Bioengineering

Neisseria gonorrhoeae: the bacteria that cause gonorrhea

Last, but definitely not least, is Neisseria gonorrhoeae, which are bacteria that can infect the mouth, throat, rectum, urethra, cervix, and even eyes.

Gonococci, as these bacteria are called, have an appendage that is akin to a grappling hook — it attaches to a surface and then retracts, pulling the bacterium into contact with the host cell, to which it can easily adhere. These retractile appendages, which are usually bundled together for extra strength, can pull 100,000 times the weight of the bacterium, making N. gonorrhoeae among the strongest living organisms — proportionally, it is the equivalent of a human lifting 10,000 tons. The bacteria collectively use their strong pili to pull on the host cell’s surface and invade it — where the gonococci are able to hide from the immune system.

Additionally, gonococci have been performing some genetic gymnastics lately to defeat almost every drug we’ve thrown at it. We douse it with certain antibiotics, and the bacterium literally spits them back out at us, and it inactivates other drugs by snapping the active molecules in half. Gonococci have a knack for swapping genes with living microbes, as well as scavenging DNA from dead microbes, and incorporating the genes into their own genomes. And, as gonococci have amassed a collection of antibiotic-resistance genes over the decades, gonorrhea is becoming more and more difficult to treat. Some health officials worry that, in time, many cases of gonorrhea could be incurable.


Sexuality is taboo in our culture. Most of us would be embarrassed to talk about a pharyngeal gonorrhea infection, but wouldn’t blink at mention of a case of strep throat. Some people are so affected by this cultural stigma that they avoid STD screening — sometimes even in the face of symptoms, hoping that if they ignore them, they’ll go away. This fear or embarrassment can make it difficult for people to talk to their partners about their sexual history or practicing safer sex. And practicing safer sex is important: With the consistent and correct use of condoms, your risk of transmitting or catching syphilis, chlamydia, or gonorrhea plummets!

So why am I presenting a bunch of STDs as a compilation of fun facts? It might seem flippant, but I’m hoping to show that sexually transmitted infections, just like any other infection, has a pathogen behind it: a virus, a bacteria, or some other microscopic organism — and these organisms can be fascinating! If I can get people talking about these kinds of “fun facts,” then maybe I can help them get one step closer to talking about STD screening with their partners without embarrassment. If knowing that cute and cuddly koalas can get chlamydia helps you get tested, then I’ve done my job.


Click here to check out other installments of our monthly STD Awareness series!

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