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Phenotypic phase variation in Haemophilus somnus lipooligosaccharide during bovine pneumonia and after in vitro
T J Inzana1, R P Gogolewski, L B Corbeil
1Department of Pathobiology, Virginia-Maryland Regional College of Veterinary Medicine, Blacksburg 24061.
Abstract:
A high rate of phenotypic variation in the lipooligosaccharide (LOS) electrophoretic profile of Haemophilus somnus occurred in most isolates obtained at approximately weekly intervals from three calves intrabronchially challenged with a cloned isolate of H. somnus 2336. Daily subculturing for 2 weeks resulted in at least one major alteration in the LOS electrophoretic profiles for strain 2336 and both additional disease isolates examined, but no change occurred in the LOS electrophoretic profiles for any of three commensal isolates examined. None of the LOSs from any of the postchallenge intrabronchial isolates reacted with rabbit antiserum to the challenge strain LOS in immunoblotting, but LOSs from two nasopharyngeal isolates did. Antigenic variation in the extracted LOSs of most of the isolates was supported by the results of an enzyme-linked immunosorbent assay. Preimmune serum from each of the calves did not react with any of the isolates or the challenge strain, whereas sera obtained 35 days after challenge reacted with the challenge strain and zero to five additional isolates and sera obtained 74 days after challenge reacted with two to six additional isolates. Recognition of LOSs from isolates obtained near the end of the 70-day experiment by day-74 sera was related to clearance of the bacteria from the lungs. Isolates demonstrating major electrophoretic changes showed variations in the composition of the oligosaccharide, but not lipid A, moiety of their LOSs. The oligosaccharide of the LOS of each isolate was composed predominantly of glucose but varied substantially in the contents of galactose, arabinose, xylose, mannose, and 3-deoxy-D-manno-octulosonic acid. Therefore, the LOS of H. somnus is capable of undergoing compositional and antigenic variations, which may act as an important virulence mechanism for evading host immune defense mechanisms.
Insights
Haemophilus somnus lipooligosaccharide (LOS) shows significant phenotypic variation, potentially aiding immune evasion. This bacterial adaptation may be a key virulence factor in host defense mechanisms.
Area of Science:
- Veterinary Microbiology
- Bacterial Pathogenesis
- Immunology
Background:
- Haemophilus somnus is an important pathogen in cattle, causing respiratory and reproductive diseases.
- Lipooligosaccharide (LOS) is a major surface antigen of Gram-negative bacteria and plays a crucial role in host-pathogen interactions.
- Phenotypic and antigenic variation of bacterial surface molecules can be a mechanism for immune evasion.
Purpose of the Study:
- To investigate the phenotypic and antigenic variation of Haemophilus somnus lipooligosaccharide (LOS) in response to host challenge.
- To determine if LOS variation contributes to the virulence and immune evasion strategies of H. somnus.
Main Methods:
- Electrophoretic analysis of LOS profiles from H. somnus isolates.
- Immunoblotting and enzyme-linked immunosorbent assay (ELISA) to assess antigenic variation.
- Analysis of LOS oligosaccharide and lipid A composition.
Main Results:
- High rates of phenotypic variation in LOS electrophoretic profiles were observed in H. somnus isolates from challenged calves.
- Significant antigenic variation in LOS was detected using immunoblotting and ELISA, with isolates showing altered reactivity to antisera.
- Variations in LOS composition primarily involved the oligosaccharide moiety, with changes in sugar content, but not lipid A.
Conclusions:
- Haemophilus somnus exhibits significant compositional and antigenic variation in its lipooligosaccharide.
- LOS variation in H. somnus likely serves as a critical virulence mechanism for evading host immune defenses.
- Understanding LOS variation is crucial for developing effective control strategies against H. somnus infections.