The protected physiological status of intracellularSalmonella entericapersisters reduces host cell-imposed stress

Abstract

Today, we are faced with increasingly occurring bacterial infections that are hard to treat and often tend to relapse. These recurrent infections can occur possibly due to antibiotic-tolerant persister cells. Antibiotic persistent bacteria represent a small part of a bacterial population that enters a non-replicating (NR) state arising from phenotypic switching. Intracellularly, after uptake by phagocytic cells, Salmonella enterica serovar Typhimurium (STM) forms persister cells that are able to subvert immune defenses of the host. However, the clear physiological state and perceptual properties are still poorly understood and many questions remain unanswered. Here we describe further development of fluorescent protein-based reporter plasmids that were used to detect intracellular NR persister cells and monitor the expression of stress response genes via extensive flow cytometric analyses. Moreover, we performed extensive measurements of the metabolic properties of NR STM at the early course of infection. Our studies demonstrate that NR STM persister cells perceive their environment and are capable respond to stress factors. Since persisters showed a lower stress response compared to replicating (R) STM, which was not a consequence of a lower metabolic capacity, the persistent status of STM serves as protective niche. Furthermore, up to 95% of NR STM were metabolically active at the beginning of infection additionally showing no difference in the metabolic capacity compared to R STM. The accessory capability of NR STM persisters to sense and to react to stress with constant metabolic activity may supports the pathogen to create a more permissive environment for recurrent infections.

Fluorescent protein‐based reporters reveal stress response of intracellularSalmonella entericaat level of single bacterial cells

“…It will be of interest for further research to identify host stimuli such as stressors that act on the expression of the virulence factor for manipulation of host cells. The dual colour reporter approach in combination with FC analyses will be instrumental to detect such events, and should provide access to the very small subpopulation of persister cells (Schulte, Olschewski, & Hensel, 2021). A future perspective is the recovery of distinct subpopulations of intracellular Salmonella by fluorescence‐assisted cells sorting and global analyses by transcriptomic or proteomic approaches.…”