Characterization of Histophilus somni sialic acid uptake mutant (¿nanP-¿nanU) using a mouse septicemia and mortality model

Authors: MENGHWAR, HARISH - Oak Ridge Institute For Science And Education (ORISE); Tatum, Fred; Briggs, Robert; Kanipe, Carly; Casas, Eduardo; Kaptur, Jean; Kaplan, Bryan; INZANA, THOMAS - Long Island University; AZADI, PARASTOO - University Of Georgia; Dassanayake, Rohana

Submitted to: Microbial Pathogenesis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2024
Publication Date: 8/7/2024
Citation: Menghwar, H., Tatum, F.M., Briggs, R.E., Kanipe, C.R., Casas, E., Kaptur, J.A., Kaplan, B.S., Inzana, T.J., Azadi, P., Dassanayake, R.P. 2024. Characterization of Histophilus somni sialic acid uptake mutant (¿nanP-¿nanU) using a mouse septicemia and mortality model. Microbial Pathogenesis. 194. Article 106839. https://doi.org/10.1016/j.micpath.2024.106839.
DOI: https://doi.org/10.1016/j.micpath.2024.106839

Interpretive Summary: Histophilus somni is one of the major opportunistic pathogens involved in the development of bovine respiratory disease complex (BRDC). Lipoolysaccharide (LOS, endotoxin) of H. somni is decorated with sialic acid and the bacterium can camouflage from the host immunological responses. Sialic acids are nine-carbon amino sugars found in both prokaryotes and eukaryotes. Although sialic acid is a known virulence factor, the significance of sialic acid in H. somni virulence in an animal model has not been investigated. In this study, we investigated the contribution of sialic acid to virulence by constructing H. somni sialic acid uptake mutant ('nanP-'nanU) and comparing parent and mutant strains in a mouse septicemia and mortality model. Contrary to our expectation, only a mild attenuation of H. somni infection was observed in mice. Additionally, sialic acid was found in LOS prepared from both parent and mutant bacteria. These findings suggest the possibility of existence of de novo sialic acid synthesis pathway in H. somni.

Technical 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 lipoolysaccharide (LOS), and sialylated H. somni is more resistant to phagocytic and serum-killing 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 H. somni sialic acid uptake mutant ('nanP-'nanU) and comparing parent and mutant strains in a mouse septicemia and mortality model. Intraperitoneally inoculated with wildtype H. somni (1 × 108 colony forming units/mouse, CFU) was lethal to all animals and contrary to our expectation, mice challenged with three differering doses of an H. somni 'nanP-'nanU sialic acid uptake mutant, given at 1, 2, or 5 × 108 CFU/mouse exhibited survival rates of 90%, 60%, and 0% respectively. High-performance anion exchange chromatography analyses revealed that LOS prepared from both parent and the 'nanP-'nanU 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 lack of attenuation in mouse is most likely attributed to the sialylated LOS of H. somni nanPU MT.