• Salmonella persisters undermine host immune defenses during antibiotic treatment.

      Stapels, Daphne A C; Hill, Peter W S; Westermann, Alexander J; Fisher, Robert A; Thurston, Teresa L; Saliba, Antoine-Emmanuel; Blommestein, Isabelle; Vogel, Jörg; Helaine, Sophie; HIRI, Helmholtz-Institut für RNA-basierte Infektionsforschung, Josef-Shneider Strasse 2, 97080 Würzburg, Germany. (American Association for the Advancement of Science, 2018-12-07)
      Many bacterial infections are hard to treat and tend to relapse, possibly due to the presence of antibiotic-tolerant persisters. In vitro, persister cells appear to be dormant. After uptake of Salmonella species by macrophages, nongrowing persisters also occur, but their physiological state is poorly understood. In this work, we show that Salmonella persisters arising during macrophage infection maintain a metabolically active state. Persisters reprogram macrophages by means of effectors secreted by the Salmonella pathogenicity island 2 type 3 secretion system. These effectors dampened proinflammatory innate immune responses and induced anti-inflammatory macrophage polarization. Such reprogramming allowed nongrowing Salmonella cells to survive for extended periods in their host. Persisters undermining host immune defenses might confer an advantage to the pathogen during relapse once antibiotic pressure is relieved.
    • SPI2 T3SS effectors facilitate enterocyte apical to basolateral transmigration of -containing vacuoles .

      Fulde, Marcus; van Vorst, Kira; Zhang, Kaiyi; Westermann, Alexander J; Busche, Tobias; Huei, Yong Chiun; Welitschanski, Katharina; Froh, Isabell; Pägelow, Dennis; Plendl, Johanna; et al. (Taylor & Francis, 2021-09-20)
      Salmonella pathogenicity island (SPI) 2 type three secretion system (T3SS)-mediated effector molecules facilitate bacterial survival in phagocytes but their role in the intestinal epithelium in vivo remains ill-defined. Using our neonatal murine infection model in combination with SPI2 reporter technology and RNA-Seq of sorted primary enterocytes, we demonstrate expression of SPI2 effector molecules by intraepithelial Salmonella Typhimurium (S. Typhimurium). Contrary to expectation, immunostaining revealed that infection with SPI2 T3SS-mutants resulted in significantly enlarged intraepithelial Salmonella-containing vacuoles (SCV) with altered cellular positioning, suggesting impaired apical to basolateral transmigration. Also, infection with isogenic tagged S. Typhimurium strains revealed a reduced spread of intraepithelial SPI2 T3SS mutant S. Typhimurium to systemic body sites. These results suggest that SPI2 T3SS effector molecules contribute to enterocyte apical to basolateral transmigration of the SCV during the early stage of the infection.