Characteristics of a haemolytic extract from avian Pasteurella multocida
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1Veterinary Pathology and Anatomy, School of Veterinary Science and Animal Production, The University of Queensland, Brisbane, Australia.
Abstract:
In experimental fowl cholera, the intramuscular inoculation of Pasteurella multocida induces tissue damage that implies proteolytic or cytolytic activity of the bacteria. Such activity could not be demonstrated by conventional in vitro tests. The treatment of P. multocida strain VP21 with Tween-80 yielded an extract that lysed washed chicken red cells. Extracts were active to a maximum titre of 64. Haemolytic activity of the extract was neither affected by boiling nor by extremes of pH, indicating the active component was not a simple protein. Treatment with trypsin had no effect, but it was inactivated by Proteinase K. Yields were highest from bacteria grown in dextrose starch- or casein sucrose-yeast broths; were similar if cultured in air or anaerobically, but were reduced if the bacteria were grown in 5% CO(2). Haemolytic activity was eliminated on exposure to serum or serum albumen. The extract from strain VP21 haemolysed red cells from the chicken, rabbit, sheep, horse, bovine and human, with the highest titres observed on chicken cells. Six other avian strains and seven out of 10 strains of P. multocida from other species yielded an extract which haemolysed chicken red cells. The elaboration of this cytotoxic substance in vivo and its role in pathogenesis remains to be determined.
Insights
Researchers discovered a substance from Pasteurella multocida that causes red blood cell lysis. This cytotoxic factor, found in fowl cholera bacteria, may play a role in disease pathogenesis.
Area of Science:
- Veterinary Microbiology
- Bacterial Pathogenesis
Background:
- Fowl cholera, caused by Pasteurella multocida, leads to tissue damage suggesting bacterial enzymatic activity.
- Conventional in vitro tests failed to demonstrate this proteolytic or cytolytic activity.
Purpose of the Study:
- To investigate the cytolytic activity of Pasteurella multocida.
- To characterize the substance responsible for red blood cell lysis.
Main Methods:
- Extraction of Pasteurella multocida strain VP21 using Tween-80.
- Testing haemolytic activity against various red blood cells.
- Assessing the stability of the haemolytic factor under different conditions (pH, heat, enzymes, serum).
- Screening other Pasteurella multocida strains for similar activity.
Main Results:
- An extract from P. multocida strain VP21 demonstrated haemolytic activity against chicken red blood cells (max titre 64).
- The active component was heat-stable, pH-extremes resistant, and inactivated by Proteinase K but not trypsin, suggesting a non-protein nature.
- Haemolytic activity was abolished by serum or serum albumin.
- Extracts from other avian and non-avian P. multocida strains also showed haemolytic potential.
Conclusions:
- Pasteurella multocida produces a cytotoxic substance capable of lysing red blood cells.
- The exact nature and in vivo role of this cytotoxic substance in fowl cholera pathogenesis require further investigation.
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