The Genus Pasteurella
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The Genus Pasteurella HENRIK CHRISTENSEN AND MAGNE BISGAARD
Introduction Members of the bacterial genus Pasteurella usually are regarded as opportunistic, secondary invaders in vertebrates. Pasteurella multocida is the only representative of the genus regarded as a major pathogen. Most taxa represent opportunistic invaders that might inhabit the mucosal membranes of the upper respiratory and lower genital tracts of mammals and birds. For most taxa, the pathogenic potential is unknown. The genus Pasteurella includes nine named species (P. multocida, P. canis, P. stomatis, P. dagmatis, P. gallinarum, P. avium, P. volantium, P. langaa and P. anatis) and two unnamed taxa (Pasteurella species A and species B), all referred to as Pasteurella sensu stricto. The type species of the genus P. multocida has been separated into three subspecies, P. multocida subsp. multocida, P. multocida subsp. gallicida and P. multocida subsp. septica. In addition, excluding seven species of Pasteurella ([P.] aerogenes, [P.] pneumotropica, [P.] trehalosi, [P.] caballi, [P.] mairii, [P.] bettyae and [P.] testudinis) from Pasteurella has been suggested; however, their names have not been formally changed and the genus name of these species is consequently denoted in brackets. General reference is made to Pasteurella sensu stricto.
Phylogeny The phylogeny of the genus Pasteurella has been investigated by 16S rRNA sequence comparison and rRNA-DNA hybridization (DeLey et al., 1990; Dewhirst et al., 1992; Dewhirst et al., 1993; Olsen et al., 2003). The phylogenetic position of members of Pasteurella is shown by analysis of the 16S rRNA sequences of well characterized strains of Pasteurellaceae; however, it remains to be demonstrated that these strains also represent the genetic core of the respective taxa. Thirteen monophyletic groups were recognized in addition to ten taxa not belonging to any group (Fig. 1). Except for the position of “Testudinis” as an out-group, the relative order of these groups and
of the single taxa not included in groups could not be determined. The type species P. multocida and the species P. canis, P. stomatis, P. dagmatis, and the unnamed taxon Pasteurella species B form the monophyletic core-group of Pasteurella sensu stricto (cluster 3B of Dewhirst et al. [1993] and cluster 12 of Olsen et al. [2003]). The two subspecies multocida and gallicida of P. multocida have identical 16S rRNA sequences, and only the sequence of the type strain of P. multocida was included in the analysis. The close phylogenetic relationship between the three subspecies of P. multocida and P. canis has been confirmed by phylogenetic analysis of the atpD gene sequence (Petersen et al., 2001a). The avian species, P. gallinarum, P. avium, P. volantium and Pasteurella species A, form a separate monophyletic group (cluster 3A of Dewhirst et al., 1993) along with the type strain of [Haemophilus] paragallinarum (the brackets indicate that the species is not a true member of genus Haemophilus; Mutters et al.,
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