Full text loading...
Chapter 39 : Evolution of Neisseria and Neisseria Infections
Category: Fungi and Fungal Pathogenesis; Bacterial Pathogenesis
Ebook: Choose a downloadable PDF or ePub file. Chapter is a downloadable PDF file. File must be downloaded within 48 hours of purchase
The N. meningitidis portal of entry is the nasopharynx. Asymptomatic carriage is the most frequent outcome of bacterial colonization, with transmission from host to host occurring through airborne salivary droplets. Secondary localization may occur if the bacteria crosses body barriers such as the blood-brain barrier to infect the subarachnoidal space, leading to meningitis, the most frequent meningococcal disease. As with other bacterial species, Neisseria undergo asexual haploid reproduction, although the frequent DNA transformation and recombination that occur between Neisseria species are responsible for localized gene exchanges. The development of this "sexual behavior" may be the result of the coevolution of pathogenic Neisseria as an obligate parasite of humans. The critical step in the development of pathogenic Neisseria infection takes place at the surface of epithelial cells. Pathogenic Neisseria strains usually release outer membrane vesicles (blebs) that contain large amounts of surface bacterial components. Contact between pathogenic Neisseria strains and viable target cells promotes the effective adhesion process through type IV pili, filamentous structures at the bacterial surface, crossing the N. meningitidis capsule. Iron acquisition on mucosal surfaces and in blood is crucial for neisserial virulence. The continuous shuffling and recombination of genes instead of the appearance of mutations are major traits in neisserial evolution. Evolution by tinkering should lead to genomic plasticity and the differential use of the same genes.
Electron micrographs and representations of neisserial surface structures involved in the informative talk between bacteria and target cells.
Interaction between N. meningitidis and epithelial target cells starts by the initial adhesion mediated by type IV pili. Subsequently, the bacteria interact intimately with the cellular membrane and the microvilli disappear. Bacteria can be observed inside the target cell.