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Published on: July 29, 2022
Characterization of Histophilus somni sialic acid uptake mutant (ΔnanP-ΔnanU) using a mouse septicemia and mortality
Harish Menghwar1, Fred M Tatum2, Robert E Briggs2
1Ruminant Diseases and Immunology Research Unit, United States Department of Agriculture, Agricultural Research Service, National Animal Disease Center, Ames, IA USA; Oak Ridge Institute for Science and Education (ORISE), ARS Research Participation Program, Oak Ridge, TN, USA.
Abstract:
Histophilus somni is an important pathogen of the bovine respiratory disease complex, yet the mechanisms underlying its virulence remain poorly understood. It is known that H. somni can incorporate sialic acid into lipooligosaccharide (LOS), and sialylated H. somni is more resistant to phagocytosis and complement-mediated killing by serum compared to non-sialylated bacteria in vitro. However, the virulence of non-sialylated H. somni has not been evaluated in vivo using an animal model. In this study, we investigated the contribution of sialic acid to virulence by constructing an H. somni sialic acid uptake mutant (ΔnanP-ΔnanU) and comparing the parent and mutant strains in a mouse septicemia and mortality model. Intraperitoneal challenge of mice with wildtype H. somni (1 × 108 colony forming units/mouse, CFU) was lethal to all animals. Mice challenged with three different doses (1, 2, or 5 × 108 CFU/mouse) of an H. somni ΔnanP-ΔnanU sialic acid uptake mutant exhibited survival rates of 90 %, 60 %, and 0 % respectively. High-performance anion exchange chromatography analyses revealed that LOS prepared from both parent and the ΔnanP-ΔnanU mutant strains of H. somni were sialylated. These findings suggest the presence of de novo sialic acid synthesis pathway, although the genes associated with de novo sialic acid synthesis (neuB and neuC) were not identified by genomic analysis. The lower attenuation in mice is most likely attributed to the sialylated LOS of H. somni nanPU mutant.
Insights
Histophilus somni uses sialic acid to resist immune defenses. A mutant lacking sialic acid uptake was less virulent in mice, suggesting sialic acid contributes to H. somni pathogenesis.
Area of Science:
- Bacteriology
- Immunology
- Veterinary Medicine
Background:
- Histophilus somni causes bovine respiratory disease.
- Sialic acid incorporation into lipooligosaccharide (LOS) enhances bacterial resistance to host defenses in vitro.
- The in vivo role of sialic acid in H. somni virulence is unknown.
Purpose of the Study:
- To investigate the contribution of sialic acid to H. somni virulence in vivo.
- To evaluate the virulence of a sialic acid uptake mutant in a mouse model.
Main Methods:
- Construction of an H. somni sialic acid uptake mutant (ΔnanP-ΔnanU).
- Comparison of wildtype and mutant H. somni virulence in a mouse septicemia and mortality model.
- Analysis of lipooligosaccharide (LOS) sialylation using high-performance anion exchange chromatography.
Main Results:
- Wildtype H. somni was lethal to all mice upon intraperitoneal challenge.
- The H. somni ΔnanP-ΔnanU mutant showed reduced virulence, with survival rates of 90%, 60%, and 0% at different challenge doses.
- Both wildtype and mutant H. somni strains exhibited sialylated LOS, suggesting an alternative sialic acid synthesis pathway.
Conclusions:
- Sialic acid incorporation into LOS contributes to H. somni virulence in a mouse model.
- The H. somni nanPU mutant's residual virulence is likely due to sialylated LOS from de novo synthesis.
- Further investigation is needed to identify the genes responsible for de novo sialic acid synthesis in H. somni.
