STD Awareness: Genetics and the Gonococcus

Image: CDC

Ever since the discovery of effective antibacterial therapies less than a century ago, humans have been able to easily cure gonorrhea, the sexually transmitted scourge that laid waste to fallopian tubes and robbed newborns of vision. Most of us in the developed world have forgotten that this disease was once a leading cause of infertility in women and blindness in babies — and still is in much of the developing world.

Unfortunately, gonococci — the species of bacteria that cause gonorrhea — have been evolving resistance to every antibiotic we’ve thrown at them, including sulfonamides, penicillins, tetracyclines, macrolides, fluoroquinolones, and narrow-spectrum cephalosporins. We have one remaining first-line gonorrhea treatment left: extended-spectrum cephalosporins, which include cefixime, which is taken orally, and ceftriaxone, which is administered as a shot — and resistance is emerging to those drugs, as well.

Gonococci don’t swap potato salad recipes at family reunions — they swap genetic material!

The emergence of antibiotic-resistant gonorrhea is considered one of the most pressing problems in infectious disease — just two years ago, the Centers for Disease Control and Prevention named it an “urgent threat,” and indeed, gonorrhea seems to be evolving resistance to drugs at quite a rapid clip. Gonococci can acquire resistance to antibiotics in three ways.

First, a genetic mutation can endow bacteria with special antibiotic-fighting powers, making it harder for a drug like penicillin to attach to their cells and destroy them. Such a mutant is more likely to gain evolutionary traction if it finds itself in an antibiotic-drenched environment in which resistance to that drug allows it to “outcompete” other bacteria. Indeed, antibiotic resistance was first documented in the 1940s, just years after sulfonamides and penicillin were introduced as the first effective cures for gonorrhea.

Second, in a process called transformation, gonococci can easily scavenge DNA from their surroundings and incorporate it into their own genomes. When they come across some DNA — say, from a dead bacterium — they are able to take it into their cells and patch long segments of foreign genes into their own DNA. In so doing, they are able to create genetic hybrids between their own genes and those of other organisms — usually other gonococci, but sometimes related Neisseria organisms, and rarely unrelated species.

A bacterium (left) uses an appendage called a sex pilus to transfer copies of genes to a second bacterium. Bacteria can transfer genes that confer antibiotic resistance to one another.

An E. coli bacterium (left) uses an appendage called a sex pilus to transfer copies of genes to a second bacterium.

Third, some gonococci are able to engage in “conjugation,” which is essentially bacteria sex! During conjugation, one bacterium uses an appendage called a sex pilus to attach to another bacterium and deliver a circular piece of DNA from the donor to the recipient. The recipient is now in possession of any traits its new DNA encodes.

You know how we humans are officially Homo sapiens? The scientific name for gonococci is Neisseria gonorrhoeae. And, just as we had genetic “cousins” in the form of Homo neanderthalensis (aka the Neanderthals), so too do Neisseria gonorrhoeae have cousins in the Neisseria genus. Most human-associated Neisseria species don’t cause disease, and live peacefully in our upper respiratory tracts. These species include Neisseria flavescensNeisseria flavaNeisseria perflavaNeisseria mucosaNeisseria siccaNeisseria polysaccharea, and more.

When gonococci meet their cousins at a family reunion, they don’t swap recipes for potato salad — they swap genetic material. For example, Neisseria subflava can wield genes that give them resistance to the antibiotics penicillin, cephalosporin, tetracycline, and ciprofloxacin. If a gonococcus drops by for a visit in a person’s throat, its cousin can share resistance genes to help it evade the next douse of antimicrobial drugs. This is one reason why it’s so important to use antibiotics sparingly and correctly! Failing to do so can increase the chances that bacteria will develop resistance.

If you are sexually active, it’s best to avoid getting gonorrhea in the first place. First, know your STD status and your partner’s STD status! It’s a great idea to get tested for STDs with your partner — it can help you get your relationship on good footing by getting a possibly difficult conversation out of the way. Second, practice safer sex — especially if you don’t know your partner’s STD status. If a penis is involved in your sexual activities, put a condom on it! Yes, even for oral sex. Dental dams and other barriers can be used over the anus or vagina to reduce the risk of STD transmission during anilingus (oral-anal contact) and cunnilingus (oral-vaginal contact).

It may only be a matter of time until one novel antibiotic-resistant strain of gonococci outpaces them all, equipped with both extensive multidrug resistance and the biological fitness necessary to run rampant in susceptible populations. The wily gonococcus is capable of mutations, transformations, and conjugations that confer extensive resistance to antibiotics, and our pharmaceutical arsenal is rapidly dwindling. As we say at Planned Parenthood Arizona, use condom sense!

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