Beating Chlamydia at Its Own Game

Scientists from the University of Washington have unraveled the mystery of how Chlamydia bacteria bind to and infect host cells. The finding, reported in the current issue of the Journal of Clinical Investigation, could open the door to finding a cure for chlamydia, a sexually transmitted disease that strikes more than 50 million people worldwide each year.

It's well known that the Chlamydia trachomatis bacterium settles into its host by attaching itself to the cells it infects, but pathobiologist Cho-Chou Kuo and his colleagues wanted to know more about its viruslike modus operandi. More than a decade ago, Kuo had found evidence for a glycoprotein--a molecule consisting of a protein fused to a carbohydrate backbone--that made up part of the bacteria's outer membrane. Kuo wanted to explain how this glycoprotein adhered to the host cell. Using a mapping technique developed in Japan, Kuo and his colleagues found an answer by isolating and identifying a carbohydrate, present in very small quantities, that he believes mediates Chlamydia's attachment to the host cells.

The next step was to beat Chlamydia at its own game. By flooding potential host cells in vitro with a decoy sugar before introducing the Chlamydia bacteria into the cells, Kuo says, "there was no place for the Chlamydia to attach to." As a result, the cells remained uninfected.

But blocking a sugar may not be the sweet solution Kuo envisions. Gerald Byrne, a University of Wisconsin microbiologist, says that not everyone in the field is convinced that Chlamydia even has glycoproteins, which are rarely present in bacteria. And there are other possible explanations for how Chlamydia interacts with host cells. Still, Byrne believes "there's no reason that practical work can't go on."

For Kuo's team, that means trying to synthesize a carbohydrate that is just as effective but easier to work with than the natural decoy used in his experiments. Such a carbohydrate could someday be added to contraceptive gel to help reduce the spread of Chlamydia. Although the gel would only protect women, Kuo admits, "that's better than nothing."