Mechanism of bacterial infection of ticks

Before infecting humans, tick-borne bacteria or viruses first have to get past a tick's defenses to colonize it. How this occurs is not well understood. To investigate, researchers studied a model of the second-most-common tick-borne infection in the United States, human granulocytic anaplasmosis, which can cause headaches, muscle pain, and even death.

The researchers found that in ticks, the bacterium that causes the infection, A. phagocytophilum, triggers the expression of a particular protein. This protein alters molecules in the tick's gut, allowing the bacteria to enter and colonize the gut microbes.

A. phagocytophilum induces ticks to express Ixodes scapularis antifreeze glycoprotein (iafgp), which encodes a protein with several properties, including the ability to alter bacterial biofilm formation. IAFGP thereby perturbs the tick gut microbiota, which influences the integrity of the peritrophic matrix and gut barrier—critical obstacles for Anaplasma colonization.

Mechanistically, IAFGP binds the terminal D-alanine residue of the pentapeptide chain of bacterial peptidoglycan, resulting in altered permeability and the capacity of bacteria to form biofilms.
"It's like a stealth warrior that indirectly changes the tick by using the tick's own defense system," said senior author of the study.

The unexpected finding could help scientists develop strategies to block A. phagocytophilum and other tick-borne agents that cause disease, say the researchers. The team will explore the phenomenon in the bacterium that causes Lyme disease, and its work could have implications for other mosquito-borne infections, such as Zika and West Nile.

The study was published by the Proceedings of the National Academy of Sciences.

http://news.yale.edu/2017/01/17/how-stealth-warrior-bacteria-turn-tick-s-gut-microbes-against-itself