Molecular classification and its impact on diagnostics and understanding the phylogeny and epidemiology of selected members of Pasteurellaceae of veterinary importance.

In this paper we briefly report recent taxonomic changes that have taken place within the bacterial family Pasteurellaceae as a result of molecular investigations. We address the complexity and diagnostic possibilities and outline the current knowledge on the population structure these investigations have generated. In addition, we discuss future possibilities to improve basic understanding of genetic diversity at population level, possible host adaptation and stability of clones associated with disease outbreaks. All taxa of Pasteurellaceae have been characterized by 16S rRNA gene sequencing, and the 16S rRNA gene sequence has been the starting point for classification and identification of most taxa, including PCR detection methods developed. Generally, it is preferred to isolate and store the bacterium before characterization is carried out, however, if this is impossible, a PCR test can be carried out on DNA extracted from suspected material. Fluorescent in situ hybridization (FISH) is a possibility for only a few members of Pasteurellaceae. Identification based on the partial rpoB sequence is possible when a high simililarity to a sequence of a well known reference strain is found. Multilocus sequence typing (MLST) is only available for a few taxa of Pasteurellaceae of veterinary importance including [Haemophilus] parosuis, Mannheimia haemolytica, Pasteurella multocida and Actinobacillus pleuropneumoniae. Application of this method for characterization of broad strain collections has improved our knowledge on population level significantly, and added to our understanding of disease manifestations. Current improvements in progress focus on sequence based identification at the population level reflecting that disease and persistence, host associations and host response are expressed at the clonal population level rather than at the species level.