Antibiotic treatment of the hard tick Ixodes ricinus: Influence on Midichloria mitochondrii load following blood meal

Midichloria mitochondrii is the most prevalent symbiont of the hard tick Ixodes ricinus, present in 100% of eggs and adult females of wild ticks. This bacterium is intracellular, and is the only known symbiont able to invade the mitochondria of the host cells. However, the role that M. mitochondrii plays in the host metabolism has yet to be elucidated. Multiple lines of evidence indicate the possibility of transmission of this bacterium to the vertebrate host during the tick blood meal. In order to investigate the role of M. mitochondrii in the biology of the tick host, we performed an antibiotic treatment on Ixodes ricinus individuals, with the aim of reducing/eliminating the symbiont, and to potentially observe the dynamic of bacterial infection in the tick host. We microinjected engorged adult females of I. ricinus with tetracycline, and we allowed the resulting larvae to feed on gerbils treated with the same antibiotic. The amount of M. mitochondrii was evaluated at different stages of the experiment using molecular techniques. In addition we evaluated the presence/absence of the symbiont DNA in the blood of gerbils used for the larval feeding. The performed treatments did not allow to eliminate the symbiont population from the host tick, however it allowed to reduce the multiplication that occurs after the larval blood meal. These results open the way for future experiments, using different antibiotic molecules, different administration methods and antibiotic administration on subsequent tick stages, to fulfill the goal of eliminating M. mitochondrii from the host I. ricinus, a major step in our understanding of the impact of this bacterium on ticks.