Brucella is an intracellular bacterial pathogen that causes chronic systemic infection in domesticated livestock and poses a zoonotic infectious risk to humans. The virulence of Brucella is critically dependent on its ability to replicate and survive within host macrophages. Brucella modulates host physiological pathways and cell biology in order to establish a productive intracellular replicative niche. Conversely, the host cell presumably activates pathways that limit infection. To identify host pathways contributing to this yin and yang during host cell infection, we performed a high-throughput chemical genetics screen of known inhibitors and agonists of host cell targets to identify host factors that contribute to intracellular growth of the model pathogen Brucella neotomae. Using this approach, we identified the p38 mitogen-activated protein (MAP) kinase pathway and autophagy machinery as both a linchpin and an Achilles' heel in B. neotomae's ability to coopt host cell machinery and replicate within macrophages. Specifically, B. neotomae induced p38 MAP kinase phosphorylation and autophagy in a type IV secretion systemdependent fashion. Both p38 MAP kinase stimulation and an intact autophagy machinery in turn were required for phagosome maturation and intracellular replication. These findings contrasted with those for Legionella pneumophila, where chemical inhibition of the p38 MAP kinase pathway and autophagy factor depletion failed to block intracellular replication. Therefore, results from a chemical genetics screen suggest that intersections of the MAP kinase pathways and autophagy machinery are critical components of Brucella's intracellular life cycle. B rucella is a facultative, intracellular, Gram-negative pathogen that causes chronic systemic infection in mammals. Humans become infected through ingestion of contaminated milk, percutaneous blood exposure, or inhalation of aerosolized organisms from birthing farm animals. Infection is associated with prolonged and debilitating fever, hepatosplenomegaly, lymphadenopathy, and potentially life-threatening sequelae, including endocarditis, osteomyelitis, and meningitis (1).The VirB-based type IV secretion system (T4SS) is a major virulence determinant of Brucella spp. (2-5) and is required for intracellular replication in host macrophages. VirB mutants also show dramatically reduced virulence in experimental models. The VirB operon encodes a multiprotein molecular syringe, induced by phagosomal acidification, that translocates effector proteins from the bacterial cytoplasm across the phagosomal membrane into the host cell cytoplasm. Effectors have multiple effects on the Citation Kang Y-S, Kirby JE. 2019. A chemical genetics screen reveals influence of p38 mitogen-activated protein kinase and autophagy on phagosome development and intracellular replication of Brucella neotomae in macrophages. Infect Immun 87:e00044-19.on July 10, 2020 by guest http://iai.asm.org/ Downloaded from host cell that ultimately result in altered maturation of the bacterial phago...