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Category: Fungi and Fungal Pathogenesis; Bacterial Pathogenesis
Evolution of Haemophilus influenzae and Haemophilus Infections, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815639/9781555814144_Chap31-1.gif /docserver/preview/fulltext/10.1128/9781555815639/9781555814144_Chap31-2.gifAbstract:
The structure of the genus Haemophilus has been studied by examining the phylogeny of housekeeping genes such as the adenylate kinase gene (adk), the glucose-6-phosphate isomerase gene (pgi), and the recombination protein gene (recA). Housekeeping gene similarity supported previous DNA-DNA hybridization data for the genus rather than the phylogeny inferred from 16S rRNA gene sequence comparison. Escherichia coli and Haemophilus influenzae appear to be closely related. However, their different ways of life and their different genome sizes (from 4.7 Mb in E. coli to 1.8 Mb in H. influenzae) suggest that these two bacteria followed different paths in their recent evolutionary history after having diverged from their last common ancestor. Virulence determinants are often highly mutable compared to genes for housekeeping functions; their variability can provide clues to the nature of the selective forces driving pathogen evolution. As in other bacteria, horizontal evolution in H. influenzae occurs by the acquisition of new genetic material from transformation of native DNA, transduction by phages, or conjugation by plasmids; this new genetic material is then passed on to subsequent generations through vertical evolution. Polymorphisms in variable number of tandem repeats (VNTRs) and microsatellites may be an efficient procedure to enhance phenotypic variation in pathogenesis and the evolution of bacterial H. influenzae strains. Bacteriophages may influence the chromosomal evolution of their bacterial hosts, mediating rearrangements and the acquisition of novel genes.
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Distribution of incidence of H. influenzae invasive infections according to patient’s age after widespread vaccinations against H. influenzae type b (author’s data).
Dendrogram illustrating the genetic relationship of H. influenzae strains isolated from invasive infections, as determined by pulsed-field gel electrophoresis. H. influenzae type b isolates are much more clonal than nontypeable isolates.
Events in the evolution of Haemophilus influenzae in the last 20 years