Crossed immunoelectrophoresis applied to representative strains from 11 different Pasteurella species under taxonomic aspects

Proposed minimal standards for the description of genera, species and subspecies of the Pasteurellaceae

Principles and guidelines are presented to ensure a solid scientific standard of papers dealing with the taxonomy of taxa of Pasteurellaceae Pohl 1981. The classification of the Pasteurellaceae is in principle based on a polyphasic approach. DNA sequencing of certain genes is very important for defining the borders of a taxon. However, the characteristics that are common to all members of the taxon and which might be helpful for separating it from related taxa must also be identified. Descriptions have to be based on as many strains as possible (inclusion of at least five strains is highly desirable), representing different sources with respect to geography and ecology, to allow proper characterization both phenotypically and genotypically, to establish the extent of diversity of the cluster to be named. A genus must be monophyletic based on 16S rRNA gene sequence-based phylogenetic analysis. Only in very rare cases is it acceptable that monophyly can not be achieved by 16S rRNA gene sequence comparison. Recently, the monophyly of genera has been confirmed by sequence comparison of housekeeping genes. In principle, a new genus should be recognized by a distinct phenotype, and characters that separate the new genus from its neighbours should be given clearly. Due to the overall importance of accurate classification of species, at least two genotypic methods are needed to show coherence and for separation at the species level. The main criterion for the classification of a novel species is that it forms a monophyletic group based on 16S rRNA gene sequence-based phylogenetic analysis. However, some groups might also include closely related species. In these cases, more sensitive tools for genetic recognition of species should be applied, such as DNA-DNA hybridizations. The comparison of housekeeping gene sequences has recently been used for genotypic definition of species. In order to separate species, phenotypic characters must also be identified to recognize them, and at least two phenotypic differences from existing species should be identified if possible. We recommend the use of the subspecies category only for subgroups associated with disease or similar biological characteristics. At the subspecies level, the genotypic groups must always be nested within the boundaries of an existing species. Phenotypic cohesion must be documented at the subspecies level and separation between subspecies and related species must be fully documented, as well as association with particular disease and host. An overview of methods previously used to characterize isolates of the Pasteurellaceae has been given. Genotypic and phenotypic methods are separated in relation to tests for investigating diversity and cohesion and to separate taxa at the level of genus as well as species and subspecies.

[Pasteurella] caballi infection not limited to horses ? a closer look at taxon 42 of Bisgaard

AIM

To investigate if taxon 42 of Bisgaard isolated from pigs represents genuine [Pasteurella] caballi, which was previously only isolated from horses.

METHODS AND RESULTS

A total of 15 field isolates from horses and pigs from five different countries representing three continents were subjected to extended phenotypical characterization. Although minor differences were observed between taxon 42 and [P.] caballi, these differences did not allow phenotypic separation. Ribotyping based on HindIII digestion showed five profiles based on nine band positions. One [P.] caballi strain and two taxon 42 strains shared the same profile. Ribotyping using HpaII gave a higher diversity with nine profiles based on ten band positions. While no profiles were shared between the taxon 42 and [P.] caballi strains, pattern analysis showed that two of the taxon 42 isolates were most similar (91% similarity) with a [P.] caballi isolate. The 16S rRNA gene sequencing of one strain of taxon 42 and one strain of [P.] caballi was performed and compared with the published sequence for the type strain of [P.] caballi. The three strains showed nearly identical sequences with at least 99.8% similarity. DNA re-associations measured by the micro-well method were 79 and 77%, respectively between the type strain of [P.] caballi and two strains of taxon 42 representing distinct ribotypes and confirmed that taxon 42 belongs to [P.] caballi.

CONCLUSION

The present investigation documents that [P.] caballi can be isolated from clinical respiratory specimens from pigs and the recognized association with respiratory infections in horses and horse bite infection in humans. Strains classified as taxon 42 are [P.] caballi isolated from pigs and for both pigs and horses, lesions mainly include the respiratory tract.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results will improve the diagnostics and progress studies of virulence and epidemiology of [P.] caballi.

Investigations on the clonality of isolates ofPasteurella gallinarumobtained from turkeys in Germany

Pasteurella gallinarum has been considered an opportunistic pathogen rather than a primary pathogen for chickens. As P. gallinarum has been found to have a high genotypic diversity, one would expect a polyclonal distribution among isolates from different farms if this organism is a secondary invader. The aims of this investigation were to genetically characterize isolates obtained from outbreaks affecting several turkey farms to confirm the existence of the infection in turkeys and to investigate the genetic relationship between isolates from affected farms. A total of 17 isolates from 14 outbreaks of respiratory disease in Germany were subjected to extended phenotypic and genotypic characterization. All isolates were of the same phenotype, typical of P. gallinarum. Ribotyping of three isolates using either HpaII or HindIII showed that they had identical profiles and indicated that the isolates all originated from the same clone. Comparison with HpaII ribotypes from a previous study showed that the pattern was identical to that obtained with isolates from a Zimbabwean outbreak in chickens during 1999 to 2000. Restriction endonuclease analysis typing of 14 isolates from all 14 farms showed that they had identical profiles but these differed from those obtained with isolates from the Zimbabwean outbreak. Sequencing of the 16S rRNA gene and sequence comparisons with other Pasteurellaceae confirmed their classification as P. gallinarum. Identification of the same clone of P. gallinarum from 14 outbreaks of acute respiratory disease in turkeys within a time period of 2 months suggests a common source of infection, and that P. gallinarum probably played a primary role rather than a secondary role in the outbreaks.

Characterization of sucrose-negative Pasteurella multocida variants, including isolates from large-cat bite wounds

To validate the identification of Pasteurella multocida-like bacteria negative for acid formation from sucrose, including isolates from bite wounds caused by large cats, 17 strains were phenotypically and genotypically characterized. Phylogenetic analysis of partially sequenced rpoB and infB genes showed the monophyly of the strains characterized and the reference strains of P. multocida. The sucrose-negative strains formed two groups, one related to reference strains of P. multocida and the other related to a separate species-like group (taxon 45 of Bisgaard). DNA-DNA hybridization further documented the species-like nature of this group. Ribotyping showed the heterogeneity of all strains except four strains that shared the same ribotype and that were isolated from bovine lungs. Phylogenetic analysis by 16S rRNA sequence comparison showed the monophyly of the strains characterized and the reference strains of P. multocida. Two strains isolated from leopard bite wounds were related to the type strain of P. dagmatis; however, they represented a new taxon (taxon 46 of Bisgaard), in accordance with their distinct phenotypic and genotypic identifications. The present study documents that sucrose-negative strains of P. multocida-like bacteria belong to two genotypically distinct groups. The study further confirms the phenotypic heterogeneity of P. multocida strains and documents two new species-like taxa of Pasteurella related to P. multocida. Until diagnostic tools have been further elaborated, special care should be taken in the identification of Pasteurella-like bacteria isolated from bite wounds caused by large cats. The evidence of phenotypic and genotypic divergence calls for the further development of PCR tests and DNA sequencing to document doubtful isolates.

Revised description and classification of atypical isolates of Pasteurella multocida from bovine lungs based on genotypic characterization to include variants previously classified as biovar 2 of Pasteurella canis and Pasteurella avium

Strains deviating in key phenotypic characters, mainly isolated from cases of bovine pneumonia in five European countries, were genotyped in order to examine their genotypic relationship withPasteurella multocida. Twenty-two strains ofPasteurella aviumbiovar 2, including variants in indole, xylose and mannitol, 18 strains ofPasteurella canisbiovar 2 and variants of this taxon, five strains ofP. multocidasubsp.septicashowing variations in indole and ornithine decarboxylase, nine strains ofP. multocidasubsp.multocidashowing variation in ornithine decarboxylase and mannitol, and type strains of the subspecies ofP. multocidawere included. Ribotyping was used to examine the relationship of the strains, and 13 types, each containing between one and 20 isolates, were observed. Identical ribotypes were observed in some cases forP. aviumbiovar 2 and eitherP. canisbiovar 2 orP. multocidasubsp.septica. ITS (16S–23S rRNA internal transcribed spacer) fragment-length profiling showed identity of the majority of strains (47 of 52), representing all four taxa, with only five divergent strains. A 16S rRNA sequence comparison of 11 strains representing the main ribotype clusters showed 99·9 % similarity to the type strain ofP. multocidasubsp.multocida, but only 97·4 % similarity was obtained toP. canis(biovar 1) and 93·7 % toP. avium(biovar 1). A species-specific PCR test forP. multocidagave a positive result with biovar 2 variants ofP. aviumandP. canis. DNA–DNA hybridizations between strains ofP. multocida, biovar 2 variants ofP. aviumandP. canis, andP. multocidasubsp.septicaconfirmed similarity at the species level. It is proposed, on the basis of genotypic similarity, thatP. multocidabe reclassified to include the biovar 2 variants ofP. aviumandP. canisand that the existence of the biovar 2 variants ofP. aviumandP. canisis highly questionable. It is concluded that the redefinedP. multocidais genotypically homogeneous, although phenotypically diverse lineages exist with respect to ornithine decarboxylase, indole and mannitol, characters that have been regarded as essential for identification to the species level. A formal reclassification of the species is not possible, however, since too few strains have been found to vary in these key characters. Considering the phenotypic diversity ofP. multocida, identification will have to depend partly on genotypic methods and the source host also seems important for safe diagnosis.