The genus Yersinia has been used as a model system to study pathogen evolution. Using whole-genome sequencing of all Yersinia species, we delineate the gene complement of the whole genus and define patterns of virulence evolution. Multiple distinct ecological specializations appear to have split pathogenic strains from environmental, nonpathogenic lineages. This split demonstrates that contrary to hypotheses that all pathogenic Yersinia species share a recent common pathogenic ancestor, they have evolved independently but followed parallel evolutionary paths in acquiring the same virulence determinants as well as becoming progressively more limited metabolically. Shared virulence determinants are limited to the virulence plasmid pYV and the attachment invasion locus ail. These acquisitions, together with genomic variations in metabolic pathways, have resulted in the parallel emergence of related pathogens displaying an increasingly specialized lifestyle with a spectrum of virulence potential, an emerging theme in the evolution of other important human pathogens.genomics metabolic streamlining | pathoadaptation | Enterobacteriaceae B acterial species are defined on the basis of phenotypic characteristics, such as cellular morphology and biochemical characteristics, as well as DNA-DNA hybridization and 16S rRNA comparison. Using high-throughput whole-genome approaches we can now move beyond classic methods and develop population frameworks to reconstruct accurate inter-and intraspecies relationships and gain insights into the complex patterns of gene flux that define different taxonomic groups.Bacterial whole-genome sequencing has revealed enormous heterogeneity in gene content, even between members of the same species. From a bacterial perspective the acquisition of new genes provides the flexibility to adapt and exploit novel niches and opportunities. From a human perspective, integration of genes by bacteria has been directly linked to the emergence of new pathogenic clones, often from formerly harmless lineages (1, 2). In addition to gene gain, gene loss is also strongly associated with host restriction in acutely pathogenic bacterial species, such as Yersinia pestis and Salmonella enterica serovars, including Salmonella Typhi (3-5), where gene loss can remove functions unnecessary in the new niche (6). These specialist pathogens show a much higher frequency of functional gene loss than closely related host generalist pathogens, such as Yersinia pseudotuberculosis (7).Previous Yersinia genome studies (8, 9) have examined the evolution of pathogenicity by comparing strains from a selection of species or species subtypes within the genus, limiting our understanding of the evolutionary context of individual species. The majority of the Yersinia species are found in the environment and do not cause disease in mammals. Three species are known as human pathogens: the plague bacillus Y. pestis and the enteropathogens Yersinia enterocolitica and Y. pseudotuberculosis. SignificanceOur past understanding of pathogen evo...

Molecular typing and virulence markers were used to evaluate the genetic profiles and virulence potential of 106 Yersinia enterocolitica strains. Of these strains, 71 were bio-serotype 4/O : 3, isolated from human and animal clinical material, and 35 were of biotype 1A or 2 and of diverse serotypes, isolated from food in Brazil between 1968 and 2000. Drug resistance was also investigated. All the strains were resistant to three or more drugs. The isolates showed a virulence-related phenotype in the aesculin, pyrazinamidase and salicin tests, except for the food isolates, only two of which were positive for these tests. For the other phenotypic virulence determinants (autoagglutination, Ca ++ dependence and Congo red absorption), the strains showed a diverse behaviour. The inv, ail and ystA genes were detected in all human and animal strains, while all the food isolates were positive for inv, and 3 % of them positive for ail and ystA. The presence of virF was variable in the three groups of strains. The strains were better discriminated by PFGE than by enterobacterial repetitive intergenic consensus PCR (ERIC-PCR). A higher genomic similarity was observed among the 4/O : 3 strains, isolated from human and animal isolates, than among the food strains, with the exception of two food strains possessing the virulence genes and grouped close to the 4/O : 3 strains by ERIC-PCR. Unusually, the results revealed the virulence potential of a bio-serotype 1A/O : 10 strain, suggesting that food contaminated with Y. enterocolitica biotype 1A may cause infection. This also suggests that ERIC-PCR may be used as a tool to reveal clues about the virulence potential of Y. enterocolitica strains. Furthermore, the results also support the hypothesis that animals may act as reservoirs of Y. enterocolitica for human infections in Brazil, an epidemiological aspect that has not been investigated in this country, confirming data from other parts of the world. INTRODUCTIONYersinia enterocolitica is the most prevalent Yersinia species connected to disease in humans (Bottone, 1999; RobinsBrowne, 2001). It has also frequently been isolated from animals, food and the environment (Fredriksson-Ahomaa et al., 1999;Thoerner et al., 2003; Falcão et al., 2004).Y. enterocolitica is responsible for gastroenteritis and other syndromes in humans and animals (Bottone, 1999 biochemical and serological tests that enable the differentiation of the strains into diverse bio-serotypes (Aleksic & Bockemühl, 1999). Also, pathogenic strains are related to some phenotypic characteristics, such as pyrazinamidase production, aesculin hydrolysis, salicin fermentation, calcium dependence, autoagglutination and Congo red absorption (Bottone, 1999). Molecular genetic studies have emphasized the importance of a virulence plasmid (pYV) that encodes various virulence genes, among them virF, which is an important transcriptional regulator of other plasmid genes, as well as the role of chromosomal virulence genes that mediate cell invasion (inv and ail) and produce a therm...

SummaryMultilocus sequence analysis of 417 strains of Yersinia pseudotuberculosis revealed that it is a complex of four populations, three of which have been previously assigned species status [Y. pseudotuberculosis sensu stricto (s.s.), Yersinia pestis and Yersinia similis] and a fourth population, which we refer to as the Korean group, which may be in the process of speciation. We detected clear signs of recombination within Y. pseudotuberculosis s.s. as well as imports from Y. similis and the Korean group. The sources of genetic diversification within Y. pseudotuberculosis s.s. were approximately equally divided between recombination and mutation, whereas recombination has not yet been demonstrated in Y. pestis, which is also much more genetically monomorphic than is Y. pseudotuberculosis s.s. Most Y. pseudotuberculosis s.s. belong to a diffuse group of sequence types lacking clear population structure, although this species contains a

No abstract

No abstract