AUTHOR=Fromm Katja , Boegli Alexandra , Ortelli Monica , Wagner Alexander , Bohn Erwin , Malmsheimer Silke , Wagner Samuel , Dehio Christoph 

TITLE=Bartonella taylorii: A Model Organism for Studying Bartonella Infection in vitro and in vivo

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.913434

DOI=10.3389/fmicb.2022.913434

ISSN=1664-302X

ABSTRACT=<p><italic>Bartonella</italic> spp. are Gram-negative facultative intracellular pathogens that infect diverse mammals and cause a long-lasting intra-erythrocytic bacteremia in their natural host. These bacteria translocate <italic>Bartonella</italic> effector proteins (Beps) into host cells <italic>via</italic> their VirB/VirD4 type 4 secretion system (T4SS) in order to subvert host cellular functions, thereby leading to the downregulation of innate immune responses. Most studies on the functional analysis of the VirB/VirD4 T4SS and the Beps were performed with the major zoonotic pathogen <italic>Bartonella henselae</italic> for which efficient <italic>in vitro</italic> infection protocols have been established. However, its natural host, the cat, is unsuitable as an experimental infection model. <italic>In vivo</italic> studies were mostly confined to rodent models using rodent-specific <italic>Bartonella</italic> species, while the <italic>in vitro</italic> infection protocols devised for <italic>B. henselae</italic> are not transferable for those pathogens. The disparities of <italic>in vitro</italic> and <italic>in vivo</italic> studies in different species have hampered progress in our understanding of <italic>Bartonella</italic> pathogenesis. Here we describe the murine-specific strain <italic>Bartonella taylorii</italic> IBS296 as a new model organism facilitating the study of bacterial pathogenesis both <italic>in vitro</italic> in cell cultures and <italic>in vivo</italic> in laboratory mice. We implemented the split NanoLuc luciferase-based translocation assay to study BepD translocation through the VirB/VirD4 T4SS. We found increased effector-translocation into host cells if the bacteria were grown on tryptic soy agar (TSA) plates and experienced a temperature shift immediately before infection. The improved infectivity <italic>in vitro</italic> was correlating to an upregulation of the VirB/VirD4 T4SS. Using our adapted infection protocols, we showed BepD-dependent immunomodulatory phenotypes <italic>in vitro</italic>. In mice, the implemented growth conditions enabled infection by a massively reduced inoculum without having an impact on the course of the intra-erythrocytic bacteremia. The established model opens new avenues to study the role of the VirB/VirD4 T4SS and the translocated Bep effectors <italic>in vitro</italic> and <italic>in vivo</italic>.</p>