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Published on: January 7, 2019
Infection characteristics among Serratia marcescens capsule lineages
Mark T Anderson1, Stephanie D Himpsl1, Leandra G Kingsley1
1University of Michigan, Michigan Medicine. Department of Microbiology and Immunology. Ann Arbor, MI U. S. A.
Abstract:
Serratia marcescens is a healthcare-associated pathogen that can cause severe infections including bacteremia and pneumonia. The capsule polysaccharide of S. marcescens is a bacteremia fitness determinant and previous work defined capsule locus (KL) diversity within the species. Strains belonging to KL1 and KL2 capsule clades produce sialylated polysaccharides and represent the largest subpopulation of isolates from clinical origin. In this study, the contribution of these and other S. marcescens capsules to infection was determined in animal and cellular models. Using a murine model of primary bacteremia, clinical isolates of multiple KL types demonstrated capsule-dependent colonization of spleen, liver, and kidney following tail vein inoculation. Similar results were observed using a bacteremic pneumonia model, in that all tested strains of clinical origin demonstrated a requirement for capsule in both the primary lung infection site and for bloodstream dissemination to secondary organs. Finally, capsule from each KL clade was examined for the ability to resist internalization by bone marrow-derived macrophages. Only the sialylated KL1 and KL2 clade strains exhibited capsule-dependent inhibition of internalization, including KL2 capsule produced in a heterologous background. Together these findings indicate that lineage-specific resistance to macrophage phagocytosis may enhance survival and antibacterial defenses of clinically-adapted S. marcescens.
Insights
Serratia marcescens capsule polysaccharides are crucial for causing infections and evading immune cells. Specifically, sialylated capsules (KL1 and KL2) help bacteria resist macrophage engulfment, aiding survival in hosts.
Area of Science:
- Microbiology
- Immunology
- Infectious Diseases
Background:
- Serratia marcescens is a significant healthcare-associated pathogen.
- Its capsule polysaccharide (KL) is vital for bacteremia and exhibits diversity.
- KL1 and KL2 strains, producing sialylated polysaccharides, are common in clinical settings.
Purpose of the Study:
- To investigate the role of different Serratia marcescens capsule types in infection.
- To determine how capsules influence bacterial survival and dissemination in vivo and in vitro.
- To assess the impact of capsule structure on resistance to host immune defenses.
Main Methods:
- Murine models of primary bacteremia and bacteremic pneumonia were utilized.
- Clinical isolates of various KL types were tested for virulence and organ colonization.
- Macrophage internalization assays were performed using bone marrow-derived macrophages.
Main Results:
- Capsule was essential for S. marcescens colonization of spleen, liver, and kidney in bacteremia models.
- All tested clinical strains required capsule for lung infection and systemic spread.
- Only sialylated KL1 and KL2 capsules inhibited macrophage internalization, even in a heterologous background.
Conclusions:
- Capsule polysaccharide is a key virulence factor for Serratia marcescens.
- Sialylated KL1 and KL2 capsules confer resistance to phagocytosis by macrophages.
- Lineage-specific capsule adaptations enhance the survival and defense of clinically relevant S. marcescens strains.
