A Tale of Two Siderophores: How an Emerging Pathogen Depends on One of Its Two Siderophores for Bloodstream Infection
Gram-negative bacterial pathogens use siderophores as part of a ubiquitous iron acquisition strategy, often essential for virulence. Weakland et al. (e00117-20) characterize two siderophore systems encoded by a bacteremic isolate of Serratia marcescens, an emerging pathogen of clinical importance. While two siderophores were identified using mass spectrometry, only one, serratiochelin, significantly contributed to in vitro growth under iron-limiting conditions and to pathogenesis in vivo. The second siderophore, chrysobactin, was dispensable under these conditions. Despite differing contributions of the two siderophores to pathogenesis, both systems are highly conserved among bloodstream isolates of Serratia marcescens and likely play different roles in other niches.
Cryptococcal Glycans Modulate Host Response and Virulence
The opportunistic fungal pathogen Cryptococcus neoformans kills almost 200,000 people each year, enabled by protective virulence factors that include a xylose-rich polysaccharide capsule. Li et al. (e00288-20) show that a mutant strain that cannot localize xylose precursor molecules to the secretory pathway shows severely attenuated virulence, yet persists for many months. This mutant stimulates an altered inflammatory response that contains the fungi for extended periods and includes the formation of inducible bronchus-associated lymphoid tissue (iBALT), previously reported in only one other fungal infection. Xylose modification of cryptococcal glycoconjugates thus significantly reshapes immune recognition and host response in the context of a deadly infection.
Salmonella Persistence and Host Immunity Are Dictated by the Anatomical Microenvironment
Bacterial infections that persist systemically in host organs continue to plague the world. It is not clear why these infections manage to endure, creating a stalemate between the pathogen and a potent host immune response. In this issue, Kurtz et al. (e00026-20) show that, during an infection with the chronic enteric pathogen Salmonella enterica serovar Typhimurium, splenic anti-Salmonella helper T cells are bactericidal while liver T cells are immunosuppressive. This balance of immune activation and suppression in different systemic organs may contribute to the maintenance of Salmonella in the body and highlight the liver as a potential organ of Salmonella persistence.
Legionella pneumophila Excludes Autophagy Adaptors from the Ubiquitin-Labeled Vacuole in Which It Resides
Eukaryotic cells use a cell-autonomous defense pathway called xenophagy to direct intracellular pathogens to lysosomes for destruction. Omotade and Roy (e00793-19) demonstrate that Legionella pneumophila has evolved at least two independent mechanisms to evade host xenophagic targeting. A RavZ-dependent mechanism has the capacity to inhibit the autophagy pathway globally, which protects other intracellular pathogens from being targeted for destruction by xenophagy. A second cis-acting mechanism prevents host autophagy adaptors from recognizing the ubiquitin-labeled Legionella-containing vacuole. This cis-acting mechanism prevents poisoning of the host autophagy system to enable recognition of other xenophagic targets in the cell.
- Copyright © 2020 American Society for Microbiology.
- Top
- Article
- A Tale of Two Siderophores: How an Emerging Pathogen Depends on One of Its Two Siderophores for Bloodstream Infection
- Cryptococcal Glycans Modulate Host Response and Virulence
- Salmonella Persistence and Host Immunity Are Dictated by the Anatomical Microenvironment
- Legionella pneumophila Excludes Autophagy Adaptors from the Ubiquitin-Labeled Vacuole in Which It Resides
- Info & Metrics