Chlamydias stealthy cloaking device identified: Microbial proteins around a sexually transmitted infection allow pathogen to hide undetected inside host cells

Chlamydia, the leading cause of sexually transmitted bacterial infections, evades detection and elimination inside human cells by use of a cloaking device. But Duke University researchers have grasped the hem of that invisibility cloak and now hope they can pull it apart.

To enter the cell and peacefully reproduce, many pathogenic bacteria, including Chlamydia, cloak themselves in a piece of the cell’s membrane, forming an intracellular free-floating bubble called a vacuole or, in the case of Chlamydia, an inclusion. Chlaymydia’s cloak appears to be especially effective at evading the cell’s built-in immunity, allowing the infection to last for months.

A Duke team led by graduate student Stephen Walsh and Jörn Coers, PhD, an associate professor of molecular genetics and microbiology in the Duke School of Medicine, wanted to know how the cloaking worked.

“We knew there was the potential to kill Chlamydia, but when we did experiments with the human-adapted form, Chlamydia trachomatis, it was very good at growing in human cell cultures,” Coers said. Even after the scientists used an immune stimulant to alert the cell’s defense systems of the presence of Chlamydia, nothing happened. “We said, there’s the pathogen. Our defense system should see it. Why does it not see it?”

They ran their experiments again using a mouse-adapted version of the Chlamydia bacteria in human cells to see how the cell’s immune system responded to a non-human pathogen.

“Humans, don’t get mouse Chlamydia because it evolved with mice and human Chlamydia evolved with humans,” Coers said. “So there’s this really fine-tuned adaptation that the pathogen has undergone.” The mouse version of the bacterial inclusion was readily identified and labeled for destruction in human cells.

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