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Uptake and intracellular survival of Bordetella pertussis in human macrophages
R L Friedman1, K Nordensson, L Wilson
1Department of Microbiology and Immunology, College of Medicine, University of Arizona, Tucson 85724.
Abstract:
Recent reports have demonstrated that Bordetella pertussis has invasive behavior in vivo and in vitro. In this study, we investigated the ability of a virulent strain, avirulent mutants, and mutants deficient in specific virulence factors to enter and survive intracellularly in human macrophages in vitro. Uptake of virulent B. pertussis was dose dependent and occurred in the absence of serum or specific antibody, with entry occurring via a microfilament-dependent phagocytic process. The virulent wild-type parental strain was internalized and persisted intracellularly over the 3 days of experiments, as determined by transmission electron microscopy and by recovery of viable plate counts. This is the first report of long-term survival of B. pertussis in human macrophages. Avirulent mutants entered macrophages, but at only an average of 1.5% of virulent parental levels, and did not survive intracellularly. Mutants which did not express adenylate cyclase toxin, filamentous hemagglutinin, or pertussis toxin had decreased abilities to enter and to survive inside macrophages. The results suggest that the internalization process, as well as intracellular survival, is virulence dependent and that mutations which inactivate expression of virulence factors may affect both. The ability of B. pertussis to enter and persist inside macrophages may be important not only for survival of the bacteria but also in the pathogenesis of whooping cough.
Insights
Virulent Bordetella pertussis invades and survives long-term within human macrophages, unlike avirulent strains. This bacterial persistence and invasion ability are linked to key virulence factors, impacting whooping cough pathogenesis.
Area of Science:
- Microbiology
- Immunology
- Pathogenesis
Background:
- Recent studies indicate Bordetella pertussis exhibits invasive properties.
- Understanding bacterial interaction with host immune cells is crucial for disease pathogenesis.
Purpose of the Study:
- To investigate the capacity of virulent and avirulent Bordetella pertussis strains, including mutants lacking specific virulence factors, to enter and survive within human macrophages.
- To determine the role of bacterial virulence factors in macrophage internalization and intracellular survival.
Main Methods:
- In vitro study using human macrophages and virulent/avirulent Bordetella pertussis strains.
- Transmission electron microscopy and viable plate counts to assess bacterial entry and survival.
- Analysis of mutants deficient in adenylate cyclase toxin, filamentous hemagglutinin, or pertussis toxin.
Main Results:
- Virulent Bordetella pertussis demonstrated dose-dependent entry into macrophages via a microfilament-dependent phagocytic process.
- The virulent strain persisted intracellularly for at least 3 days, a novel finding.
- Avirulent mutants showed significantly reduced entry and no intracellular survival.
- Mutants lacking key virulence factors exhibited impaired entry and survival within macrophages.
Conclusions:
- Bordetella pertussis internalization and intracellular survival are virulence-dependent processes.
- Bacterial virulence factors play a critical role in both macrophage invasion and intracellular persistence.
- The ability of B. pertussis to survive within macrophages may contribute to its persistence and the pathogenesis of whooping cough.