The sexually transmitted infection gonorrhea has been around for centuries, described in early writings from Egypt, China and Japan. Even the bible describes warnings about “unclean discharges from the body.” Yet although the bacteria behind the infection, Neisseria gonorrhoeae, were first identified back in 1879, there are still many questions that remain unanswered about how these organisms spread from person to person.
A study in mBio this week offers clues. Researchers at Northwestern University’s Feinberg School of Medicine in Chicago and the University of Cologne in Germany have found that exposure to seminal plasma – the liquid part of semen containing secretions from the male genital tract – allows N. gonorrhoeae to more easily move and start to colonize in human tissues.
In a series of laboratory experiments, the investigators found that 24 times as much N. gonorrhoeae could pass through a synthetic barrier after being exposed to seminal plasma. In addition, exposure to seminal plasma caused hairlike appendages on the bacteria surface, called pili, to move the cells by a process known as twitching motility. This stimulatory effect could be seen even at low concentrations of seminal plasma and beyond the initial influx of seminal fluid.
Additional tests found that exposure to seminal plasma enhanced the formation of bacterial microcolonies on human epithelial cells (cells that line body cavities), which can also promote the establishment of infection.
“Our study illustrates an aspect of biology that was previously unknown,” said lead author study Mark Anderson of Northwestern. “If seminal fluid facilitates motility, it could help transmit gonorrhea from person to person.”
Today gonorrhea is the second most common sexually transmitted infection in the U.S., according to the Centers for Disease Control and Prevention, with estimates upward of 800,000 new cases each year. Fewer than half are diagnosed and reported. Untreated, gonorrhea can lead to serious and permanent health problems, including pelvic inflammatory disease in women and epididymitis, a painful condition of the testicles that may lead to infertility, in men. Untreated gonorrhea also increases a person’s risk of acquiring or transmitting HIV.
With more than 100 million estimated new cases of gonorrhea annually worldwide, said senior study author H. Steven Seifert of Northwestern, “research characterizing the mechanisms of pathogenesis and transmission of N. gonorrhoeae is important for developing new prevention strategies, since antibiotic resistance of the organism is becoming increasingly prevalent.”
Antibiotics once effective against gonorrhea, including penicillin, tetracycline and fluoroquinolones, are no longer recommended because of high rates of resistance. Only one class of antibiotics, cephalosporins including the oral antibiotic cefixime, has been left to treat the disease. But more recently, evidence from CDC’s Gonococcal Isolate Surveillance Project (GISP) suggests that cefixime, too, is becoming less effective. New gonorrhea treatment guidelines published in 2012 suggest only injectable ceftriaxone be used in combination with one of two oral antibiotics, either azithromycin or doxycycline.