The fungal pathogen Candida albicans causes macrophage death and escapes, but the molecular mechanisms remained unknown. Here we used live-cell imaging to monitor the interaction of C. albicans with macrophages and show that C. albicans kills macrophages in two temporally and mechanistically distinct phases. Early upon phagocytosis, C. albicans triggers pyroptosis, a proinflammatory macrophage death. Pyroptosis is controlled by the developmental yeast-to-hypha transition of Candida . When pyroptosis is inactivated, wild-type C. albicans hyphae cause significantly less macrophage killing for up to 8 h postphagocytosis. After the first 8 h, a second macrophage-killing phase is initiated. This second phase depends on robust hyphal formation but is mechanistically distinct from pyroptosis. The transcriptional regulator Mediator is necessary for morphogenesis of C. albicans in macrophages and the establishment of the wild-type surface architecture of hyphae that together mediate activation of macrophage cell death. Our data suggest that the defects of the Mediator mutants in causing macrophage death are caused, at least in part, by reduced activation of pyroptosis. A Mediator mutant that forms hyphae of apparently wild-type morphology but is defective in triggering early macrophage death shows a breakdown of cell surface architecture and reduced exposed 1,3 β-glucan in hyphae. Our report shows how Candida uses host and pathogen pathways for macrophage killing. The current model of mechanical piercing of macrophages by C. albicans hyphae should be revised to include activation of pyroptosis by hyphae as an important mechanism mediating macrophage cell death upon C. albicans infection. IMPORTANCE Upon phagocytosis by macrophages, Candida albicans can transition to the hyphal form, which causes macrophage death and enables fungal escape. The current model is that the highly polarized growth of hyphae results in macrophage piercing. This model is challenged by recent reports of C. albicans mutants that form hyphae of wild-type morphology but are defective in killing macrophages. We show that C. albicans causes macrophage cell death by at least two mechanisms. Phase 1 killing (first 6 to 8 h) depends on the activation of the pyroptotic programmed host cell death by fungal hyphae. Phase 2 (up to 24 h) is rapid and depends on robust hyphal formation but is independent of pyroptosis. Our data provide a new model for how the interplay between fungal morphogenesis and activation of a host cell death pathway mediates macrophage killing by C. albicans hyphae.

Macromolecular entities, such as polymers, peptides, proteins, and hybrid materials thereof, are herein reviewed as promising antibiofilm agents.

Acinetobacter baumannii is one of the most notorious hospital-acquired pathogens, and novel treatment strategies are desperately required. Two-component regulatory systems represent potential therapeutic targets as they mediate microorganism adaptation to changing environments, often control virulence, and are specific to bacteria. Here we describe the first global virulence regulator in A. baumannii. Using transcriptional profiling and functional assays of a deletion mutant in the A. baumannii sensor kinase gene, A1S_0574 (termed as gacS), we show that this sensor kinase regulates key virulence characteristics, including pili synthesis, biofilms, and motility, resulting in virulence attenuation in a mammalian septicemia model. Notably, we also identified that GacS regulates an operon novel to A. baumannii (paa operon), which is responsible for the metabolism of aromatic compounds. Deletion of paaE (A1S_1340) confirmed the role of this operon in A. baumannii virulence. Finally, we identified the cognate response regulator (A1S_0236) for GacS and confirmed their interaction. A1S_0236 was shown to regulate 75% of the GacS transcriptome and the same virulence phenotypes. Overexpression of A1S_0236 restored virulence in the gacS mutant. Our study characterizes a global virulence regulator, which may provide an alternate therapeutic target, in one of the most troublesome hospital-acquired pathogens.