Evidence of phenotypic dichotomy within an individual Pasteurella multocida type strain and among some haemorrhagic septicaemia-causing field isolates
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H J Dawkins1, A Hyatt, R B Johnson
1Regional Veterinary Laboratory, Benalla, Victoria, Australia.
Abstract:
Haemorrhagic septicaemia-causing strains of Pasteurella multocida were identified by a disease-specific ELISA. Some strains, however, were of the same serotype as those which cause haemorrhagic septicaemia (HS) but were negative when tested in the disease specific ELISA. The suspect false negative isolates were passaged in mice and retested in the HS ELISA with the same result. Immunoelectron microscopy was used to examine further these suspect HS-causing strains. Monoclonal antibodies and protein A-gold showed that the suspect negative organisms were a mixture of phenotypes with less than 10 per cent, and usually less than 2 per cent, of the population expressing HS-associated epitopes. The degree of staining on the organisms expressing the HS-epitopes was of the same intensity as the positive control organism. Expression of the HS-associated epitopes is presumably too low to allow detection in the current HS ELISA.
Insights
Certain Pasteurella multocida strains causing haemorrhagic septicaemia (HS) were missed by ELISA tests. These strains express fewer HS-associated epitopes, likely leading to false negatives in disease detection.
Area of Science:
- Veterinary Microbiology
- Immunodiagnostics
- Bacterial Pathogenesis
Background:
- Haemorrhagic septicaemia (HS) is a severe disease caused by Pasteurella multocida.
- Disease-specific enzyme-linked immunosorbent assays (ELISAs) are crucial for identifying HS-causing strains.
- Some serotypes typically associated with HS may evade current diagnostic methods.
Purpose of the Study:
- To investigate why certain Pasteurella multocida strains, serotypically similar to HS-causing ones, tested negative in a disease-specific ELISA.
- To characterize the expression of HS-associated epitopes in these suspect isolates.
Main Methods:
- Disease-specific ELISA for initial identification of Pasteurella multocida strains.
- In vivo passage in mice to re-evaluate suspect isolates.
- Immunoelectron microscopy using monoclonal antibodies and protein A-gold for epitope analysis.
Main Results:
- Several Pasteurella multocida strains, despite belonging to HS-associated serotypes, were negative in the HS ELISA.
- These negative isolates were confirmed as false negatives after mouse passage.
- Immunoelectron microscopy revealed that these strains had a low percentage (typically <2%) of cells expressing HS-associated epitopes.
Conclusions:
- The low expression of HS-associated epitopes in a subpopulation of Pasteurella multocida is likely responsible for false-negative results in the current HS ELISA.
- This finding highlights potential limitations in current diagnostic tools for haemorrhagic septicaemia.
- Further research may be needed to develop more sensitive diagnostic methods for Pasteurella multocida infections.