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Molecular aspects of virulence of Pasteurella haemolytica
A W Confer1, R J Panciera, K D Clinkenbeard
1Department of Veterinary Pathology, College of Veterinary Medicine, Oklahoma State University, Stillwater 74078.
Abstract:
Pasteurella haemolytica is represented by two biotypes (A and T), 15 serotypes, and numerous untypable strains. Specific biotypes and serotypes are associated with fibrinous pleuropneumonia (pneumonic pasteurellosis) in cattle, sheep, and goats, septicemic pasteurellosis in lambs, and mastitis in ewes. Four virulence factors have been associated with P. haemolytica: fimbriae, a polysaccharide capsule, endotoxin [lipopolysaccharide (LPS)], and leukotoxin (LKT). The interactions of these virulence factors with components of the pulmonary alveolus are discussed as a model for the pathogenesis of pasteurellosis. Fimbriae on P. haemolytica may enhance colonization of the upper respiratory tract. The capsule of P. haemolytica varies in composition among serotypes. It inhibits complement-mediated serum killing as well as phagocytosis and intracellular killing of P. haemolytica. The capsule enhances neutrophil directed migration and adhesion of P. haemolytica to alveolar epithelium. Pasteurella haemolytica LPS can alter bovine leukocyte functions, by dose-dependent inhibition or augmentation; it is directly toxic to bovine endothelium; it modifies cardiopulmonary hemodynamics; and it elevates circulatory prostanoids, serotonin, cAMP, and cGMP. Leukotoxin is produced by all known serotypes and many untypable strains. Leukotoxin is a poreforming cytolysin that affects ruminant leukocytes and platelets by altering function at low levels but causing lysis at high levels.
Insights
Pasteurella haemolytica causes severe respiratory and systemic diseases in ruminants. Its virulence factors, including leukotoxin and lipopolysaccharide, contribute to disease pathogenesis by damaging host cells and impairing immune responses.
Area of Science:
- Veterinary Microbiology
- Animal Pathology
- Ruminant Infectious Diseases
Background:
- Pasteurella haemolytica is a significant bacterial pathogen in ruminants.
- It causes diseases such as pneumonic pasteurellosis and mastitis.
- Virulence factors are key to understanding its pathogenicity.
Purpose of the Study:
- To detail the virulence factors of Pasteurella haemolytica.
- To explain the pathogenesis of pasteurellosis using these factors.
- To discuss interactions between virulence factors and host pulmonary components.
Main Methods:
- Review and discussion of existing literature on Pasteurella haemolytica virulence factors.
- Analysis of the roles of fimbriae, capsule, lipopolysaccharide (LPS), and leukotoxin (LKT).
- Examination of host-pathogen interactions at the pulmonary alveolar level.
Main Results:
- Fimbriae aid in upper respiratory tract colonization.
- The capsule inhibits phagocytosis and complement-mediated killing, promoting bacterial survival and neutrophil migration.
- LPS affects leukocyte function, damages endothelium, and alters cardiopulmonary hemodynamics.
- Leukotoxin (LKT) is a cytolysin impacting ruminant leukocytes and platelets.
Conclusions:
- Pasteurella haemolytica employs multiple virulence factors to establish infection and cause disease.
- Understanding these factors is crucial for developing effective control strategies against pasteurellosis.
- The interactions highlight a complex model for ruminant respiratory disease pathogenesis.