Ehrlichia chaffeensis DapE Is Essential for Intracellular Growth and Represents a Promising Therapeutic Target

Ehrlichia chaffeensis is an obligate intracellular bacterium that proliferates within monocytes or macrophages and causes human monocytic ehrlichiosis (HME), an emerging life-threatening zoonosis. Doxycycline is the choice of treatment for HME, yet it has prominent side effects. Host cells lack the lysine biosynthetic pathway; thus, the enzymes in this pathway are essential for bacterial growth and recognized as potential targets for the development of novel antibiotics. Here, we demonstrated that inhibitors targeting DapE, which is a key enzyme in the lysine biosynthetic pathway, especially disulfiram, effectively inhibit E. chaffeensis infection and intracellular growth. Through complementation experiments and peptide nucleic acid-mediated dapE knockdown, we showed that DapE in E. chaffeensis is functional and essential for bacterial intracellular growth. Using purified recombinant protein, we found that DapE induces IL-8 expression in host cells. Finally, we identified that NtrX, the response regulator of the two-component system NtrY/NtrX, regulates dapE expression using an electrophoretic mobility shift assay and a reporter assay. Our findings deepen the understanding of E. chaffeensis pathogenesis as well as illustrate that DapE in E. chaffeensis is a potential therapeutic target for the development of novel HME treatments.