Ehrlichia chaffeensis infections in Drosophila melanogaster.

Ehrlichia chaffeensis is an obligate, intracellular bacterium, transmitted by the tick Amblyomma americanum, and is the causative agent of human monocytic ehrlichiosis infections. We previously demonstrated that E. chaffeensis is capable of growing in Drosophila S2 cells. Therefore, we tested the hypothesis that E. chaffeensis can infect adult Drosophila melanogaster. Adult Drosophila organisms were experimentally challenged with intra-abdominal injections of bacteria. Ehrlichia-infected flies showed decreased survival compared to wild-type flies, and bacteria isolated from flies could reinfect mammalian macrophages. Ehrlichia infections activated both the cellular and humoral immune responses in the fly. Hemocytes phagocytosed bacteria after injection, and antimicrobial peptide pathways were induced following infection. Increased pathogenicity in flies carrying mutations in genes in both the Toll and Imd pathways suggests that both immune defense pathways participate in host defense. Induction of Drosophila cellular and humoral responses and the in vivo replication of E. chaffeensis suggests that D. melanogaster is a suitable host for E. chaffeensis. In the future, it will be a useful tool to unlock some of the in vivo mysteries of this arthropod-borne bacterium.