Knud Poulsen


The main theme is bacterial-host interactions in health and disease. The work focuses on the population genetics of microorganisms and their molecular epidemiology. The genetic mechanisms causing variation in bacteria and the evolution and spread of the bacterial species are studied by population genetic analyses applied to collections of bacteria isolated over time from different geographical areas and from well-defined infections combined with bacteria isolated from healthy carriers. These studies are also the basis for defining evolutionary lineages and subpopulations with different pathogenic potential. The analyses include DNA sequencing of single genes as well as whole genomes from the bacteria combined with comparative analyses of the resulting sequences. The aim is to detect genetic differences among the subpopulations which is associated with and may explain the observed differences in pathogenic potential. The effect of such putative virulence factors are tested in vitro as well as in animal models.

The projects include, among others, different Streptococcus species (e.g., S. pneumoniaeS. mitisS. agalactiae) and Aggregatibacter actinomycetemcomitans.

Among others, putative virulence factors we have analyzed include IgA1 proteases in different bacterial species, capsule production in streptococci, and leukotoxin in A. actinomycetemcomitans.

Research interests

  • To study the population genetics and molecular pathogenesis in bacterial infections and thereby to obtain a better understanding of the disease mechanisms
  • To study the interactions between bacteria and the host immune response
  • This may lead to development of better vaccines and/or treatment of the infectious diseases.


Methods in the laboratory include cultivation and isolation of bacteria , DNA based typing of bacteria,  PCR, DNA cloning and sequencing, expression and purification of recombinant proteins in E. coli, in vitro and in vivo testing of putative virulence factors.

Collaborators and centres

See recent publications.



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