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Relationship between intracellular survival in macrophages and virulence of Haemophilus influenzae type b
A E Williams1, D J Maskell, E R Moxon
1Molecular Infectious Diseases Group, John Radcliffe Hospital, Oxford, United Kingdom.
Abstract:
The phagocytosis of Haemophilus influenzae type b (Hib) by rat macrophages and the intracellular fate of ingested organisms was investigated using an acridine orange-crystal violet assay. There was a correlation between the ability of organisms to survive in macrophages in vitro and their ability to cause invasive disease. Encapsulated Hib survived and replicated within macrophages, whereas capsule-deficient mutants, although more susceptible to phagocytosis, were killed after ingestion. Differences in lipopolysaccharide also affected the ability of encapsulated Hib to survive in macrophages. The presence of viable intracellular organisms in macrophages in vivo may enhance the persistence of bacteremia and may also be important in mediating the entry of Hib into the central nervous system.
Insights
Encapsulated Haemophilus influenzae type b (Hib) survives and replicates within macrophages, unlike capsule-deficient strains. This macrophage survival correlates with Hib's ability to cause invasive disease.
Area of Science:
- Microbiology
- Immunology
- Cell Biology
Background:
- Haemophilus influenzae type b (Hib) is a significant cause of invasive bacterial disease.
- The interaction between Hib and host immune cells, particularly macrophages, is crucial for understanding disease pathogenesis.
- The intracellular fate of ingested bacteria within macrophages influences the host's ability to clear infection.
Purpose of the Study:
- To investigate the phagocytosis of Hib by rat macrophages.
- To determine the intracellular fate of ingested Hib organisms.
- To correlate bacterial survival within macrophages with the capacity to cause invasive disease.
Main Methods:
- Utilized an acridine orange-crystal violet assay to study Hib-macrophage interactions.
- Compared the survival and replication of encapsulated Hib and capsule-deficient mutants within macrophages.
- Assessed the impact of lipopolysaccharide variations on bacterial survival.
Main Results:
- Encapsulated Hib survived and replicated within macrophages.
- Capsule-deficient Hib mutants were killed after phagocytosis, despite increased susceptibility.
- Differences in lipopolysaccharide composition affected the intracellular survival of encapsulated Hib.
Conclusions:
- Bacterial survival and replication within macrophages correlate with the potential for invasive disease.
- Intracellular viable Hib within macrophages may contribute to persistent bacteremia.
- The intracellular survival of Hib in macrophages may play a role in central nervous system invasion.