Unit: Yersinia

Director: Elisabeth Carniel

The main activities of the Yersinia Research Unit include the analysis of horizontal gene transfer; bacterial evolution; molecular bases of pathogenicity; immune, physiological and genetic host responses to infection; and antibiotic resistance in pathogenic Yersinia species. Our Unit also has public health activities (French Reference Center, National Surveillance Network, and WHO Collaborating Center).

The Yersinia Research Unit was created in 2004. This Unit focuses its research activities on the genus Yersinia, which belongs to the family Enterobacteriaceae and includes three species pathogenic for humans and animals: the enteropathogens Y. pseudotuberculosis and Y. enterocolitica, and the plague agent Y. pestis.

The current activities of the Yersinia Research Unit are primarily devoted to the analysis of:

- A pathogenicity island whose presence confers to the host bacterium the ability to cause systemic infections in humans and other animals.

- The molecular bases for the exceptional pathogenicity acquired by Y. pestis since its recent emergence from Y. pseudotuberculosis.

- The pathophysiology of Yersinia infection.

- The host's mechanisms of innate and acquired immunity and the development of a plague vaccine.

- The genetic bases of susceptibility to plague.

- The resistance of pathogenic Yersinia to antibiotics and the evaluation of new treatments.

- Public health (French Reference Center, National Surveillance Network, and WHO Collaborating Center for Yersinia).

The main research works published in 2005 dealt with:

1. Horizontal transfer of the High-Pathogenicity Island of Y. pseudotuberculosis

Contributors: B. Lesic and E. Carniel.

Horizontal transfer of genetic elements plays a major role in bacterial evolution. The High Pathogenicity Island (HPI), which codes for an iron uptake system, is important for Yersinia virulence. This island is present and highly conserved in various Enterobacteriaceae, suggesting its recent acquisition by lateral gene transfer. We wanted to determine whether the HPI has kept its ability to be horizontally transmitted to new hosts. We demonstrated that the HPI is indeed transferable from a donor to a recipient Y. pseudotuberculosis strain. This transfer was observable only when the donor and recipient bacteria were co-cultured at low temperatures in a liquid medium. When optimized conditions were used, the frequency of HPI transfer reached Å10-8. The island was transferable to various serotype I strains of Y. pseudotuberculosis and to Y. pestis, but not to other serotypes of Y. pseudotuberculosis or to Y. enterocolitica. Upon transfer, the HPI was almost systematically inserted into the asn3 tRNA locus and its acquisition resulted in the loss of the resident island, suggesting an incompatibility between two copies of the HPI within the same strain. Transfer of the island did not require a functional HPI-borne insertion-excision machinery and was RecA-dependent in the recipient but not the donor strain, suggesting that integration of the island into the recipient chromosome occurs via a mechanism of homologous recombination. This lateral transfer was not restricted to the HPI but also involved adjacent sequences, leading to the mobilization of a chromosomal region, at least 46 kb in size. This study thus demonstrates that the HPI can be horizontally transmitted by a mechanism which does not require HPI-borne mobility functions.

2. Transfer of the pPla plasmid to Y. pseudotuberculosis and impact on virulence

Contributors: F. Pouillot, A. Derbise, J. Foulon and E. Carniel.

Collaborators: M. Kukkonen and T. K. Korhonen.

Y. pestis is a species that emerged recently from Y. pseudotuberculosis and gained an exceptional pathogenicity potential. One major genetic difference between the plague bacillus and its ancestor is the acquisition of the pPla plasmid, which has been associated with the increased virulence of Y. pestis. In a previous study, introduction of pPla into Y. pseudotuberculosis did not increase its virulence. However, it was subsequently demonstrated that the presence of a smooth LPS in Y. pseudotuberculosis inhibits the activity of Pla. We thus introduced pPla into a Y. pseudotuberculosis variant in which a mutation that abrogates formation of O-Ag repeats (as in natural isolates of Y. pestis) was generated. In this strain, Pla was synthesized, exported to the bacterial membrane and processed as in Y. pestis. While the ability of Pla to activate plasminogen was weak in the smooth Y. pseudotuberculosis strain, this activity was similar to that of Y. pestis in the O-Ag mutant. Furthermore, Pla-mediated inactivation of the antiprotease α2-antiplasmin was not detected at 28°C in the smooth Y. pseudotuberculosis strain but was similar to that of Y. pestis in the O-Ag mutant. Nonetheless, the Y. pseudotuberculosis O-Ag mutant harboring pPla exhibited a decreased pathogenicity upon subcutaneous infection of mice. Our results thus indicate that, although abrogation of O-side chain synthesis in a Y. pseudotuberculosis strain harboring pPla potentiates the two proteolytic activities of Pla, this is not sufficient to confer to Y. pseudotuberculosis a higher pathogenicity potential. These results also suggest that acquisition of pPla may not have been sufficient to enhance the pathogenic potential of the Y. pestis ancestor strain.

3. Diversity of Y. pseudotuberculosis strains of worldwide origin investigated by ribotyping

Contributors: E. Voskressenskaya, A. Leclercq and E. Carniel.

Collaborators: G. Tseneva.

Y. pseudotuberculosis infects a wide range of animals, including humans, and is transmitted by the fecal-oral route. This species is found globally and is responsible for human outbreaks, mainly in cold countries. In order to investigate the diversity of this species and to evaluate the potential of ribotyping for molecular typing of worldwide isolates, 80 Y. pseudotuberculosis strains isolated from various countries and different hosts, and belonging to the six classical serotypes and to nine subserotypes were analyzed. Combination of the EcoRI and EcoRV ribopatterns allowed the delineation of 27 ribotypes. In most instances, ribotypes were associated with specific subserotypes and allowed their subdivision. No association between the ribotype and the geographical origin of the strains was observed, arguing for a global spread of this organism. Similarly, no marked association between the ribotype and the type of host was noted, confirming the circulation of this pathogen in the environment, different animal species, and human hosts. Y. pseudotuberculosis exhibited ribopatterns very close to those of Y. pestis, although not completely identical. Ribotyping is thus a useful tool for molecular typing of global isolates of Y. pseudotuberculosis, but this technique has some limitations due to the small number of hybridizing bands that generate the diversity of the profiles.

4. Investigation of a fatal case of Y. enterocolitica sepsis after red blood cell transfusion

Contributors: A. Leclercq, L. Martin and E. Carniel.

Collaborators: M. Laporte Vergnes, N. Ounnoughene, J-F. Laran and P. Giraud.

Due to its ability to multiply at low temperatures in red blood cell concentrates (RBCC), Y. enterocolitica is one of the most common cause of transfusion-associated septic shock. A fatal case of septic shock occurring in a 71-year-old French patient following transfusion of a contaminated RBCC for refractory anemia was investigated. The Y. enterocolitica strains isolated from the patient's blood and the transfused RBCC were both of bioserotype 4/O:3 and had the same NotI pulsotype. High titers of antibodies against Y. enterocolitica O:3 were detected in the donor's plasma one month after blood donation. The donor reported abdominal discomfort 3.5 months prior to blood collection but had no clinical signs of intestinal infection at the time of donation. Y. enterocolitica has been identified with increased frequency as a causative agent of post-transfusion septic shock. Our nation-wide investigation of these cases led to an estimated incidence of ³ 1 case per 6.5 million RBCC distributed in France. Although rare, this often fatal complication remains non-preventable worldwide due to the lack of practical means for screening RBCC prior to transfusion.

5. National Reference Laboratory, National Surveillance network and WHO Collaborating Center for Yersinia

L. Martin, A. Leclercq, F. Guinet, and E. Carniel

See the Yersinia National Reference Laboratory web site

(http://www.pasteur.fr/sante/clre/cadrecnr/yersinia-index.html).

Keywords: Yersinia, enteropathogen, plague, virulence, genomics, physiopathology, bacteriology, immunology, public health


Activity Reports 2005 - Institut Pasteur
filet

Page Top research Institut Pasteur homepage

If you have problems with this Web page, please write to rescom@pasteur.fr