Liliane Martin

Parallel independent evolution of pathogenicity within the genus Yersinia.

Significance Our past understanding of pathogen evolution has been fragmented because of tendencies to study human clinical isolates. To understand the evolutionary trends of pathogenic bacteria though, we need the context of their nonpathogenic relatives. Our unique and detailed dataset allows description of the parallel evolution of two key human pathogens: the causative agents of plague and Yersinia diarrhea. The analysis reveals an emerging pattern where few virulence-related functions are found in all pathogenic lineages, representing key “foothold” moments that mark the emergence of these pathogens. Functional gene loss and metabolic streamlining are equally complementing the evolution of Yersinia across the pathogenic spectrum. 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.

Fatal Yersinia enterocolitica biotype 4 serovar O:3 sepsis after red blood cell transfusion

BACKGROUND: Although posttransfusion bacterial sepsis is rare, this complication is associated with a high mortality rate.

Sudden onset of pseudotuberculosis in humans, France, 2004-05.

Cases of Yersinia pseudotuberculosis infection increased in France during the winter of 2004–05 in the absence of epidemiologic links between patients or strains. This increase represents transient amplification of a pathogen endemic to the area and may be related to increased prevalence of the pathogen in rodent reservoirs.

Characterization of Atypical Isolates of Yersinia intermedia and Definition of Two New Biotypes

ABSTRACT The species Yersinia intermedia is a member of the genus Yersinia which belongs to the Enterobacteriaceae family. This species is divided into eight biotypes, according to Brenners biotyping scheme. This scheme relies on five tests (utilization of Simmons citrate and acid production from d-melibiose, d-raffinose, α-methyl-d-glucoside [αMG], and l-rhamnose). The collection of the French Yersinia Reference Laboratory (Institut Pasteur, Paris, France) contained 44 strains that were originally identified as Y. intermedia but whose characteristics did not fit into the biotyping scheme. These 44 strains were separated into two biochemical groups: variant 1 (positive for acid production from l-rhamnose and αMG and positive for Simmons citrate utlization) and variant 2 (positive for acid production from l-rhamnose and αMG). These atypical strains could correspond to new biotypes of Y. intermedia, to Y. frederiksenii strains having the atypical property of fermenting αMG, or to new Yersinia species. These strains did not exhibit growth or phenotypic properties different from those of Y. intermedia and Y. frederiksenii and did not harbor any of the virulence traits usually found in pathogenic species. DNA-DNA hybridizations performed between one strain each of variants 1 and 2 and the Y. intermedia and Y. frederiksenii type strains demonstrated that these variants do belong to the Y. intermedia species. We thus propose that Brenners biotyping scheme be updated by adding two new biotypes: 9 (for variant 1) and 10 (for variant 2) to the species Y. intermedia.

THE DETECTION OF ENZYME A OF YERSINIA ENTEROCOLITICA BY A DISC DIFFUSION METHOD

Yersinia enterocolitica has been described as expressing two types of chromosomal beta-lactamase, the broad spectrum enzyme A and the inducible cephalosporinase enzyme B. Nevertheless, not all Y. enterocolitica strains express both enzyme A and enzyme B; Y. enterocolitica strains of the less commonly isolated biotype 2, serotype O:5 (27) lack the enzyme A. Also, no other members of the Enterobacteriaceae have been demonstrated to produce enzyme A. Detection of this enzyme could therefore be a useful laboratory tool in distinguishing common pathogenic strains of Y. enterocolitica from other Enterobacteriaceae. A simple test by disc diffusion on agar for the recognition of enzyme A expression in Y. enterocolitica was evaluated. The test was based on the resistance to ticarcillin conferred by enzyme A and the highly effective inhibition of this enzyme by clavulanic acid. A typical additional zone of inhibition between the zones of inhibition around a ticarcillin 75 micrograms disc and an amoxycillin/clavulanate 3 micrograms disc was indicative of the presence of enzyme A. By contrast, a large zone of inhibition around the ticarcillin disc without an additional zone of inhibition, reflected the absence of enzyme A.

Investigation of an unusual increase in human yersinioses in Creuse, France.

OBJECTIVES To investigate an unusual cluster of Y. enterocolitica 4/O:3/VIII human infections that occurred in Creuse (France) during the summer 2008, and to perform retrospective and prospective analyses of yersiniosis cases to get a better view of the general trend. METHODS 33 pathogenic Y. enterocolitica strains isolated between 2008 and 2010 in Creuse were subjected to phenotypic and molecular typing. The database of the Yersinia National Reference Laboratory was used to compare the number of human cases over 23 years in Creuse and at the national level. RESULTS The 33 isolates had three distinct phenotypes and a high genetic diversity, ruling out a unique source of contamination. A long-term analysis of yersiniosis cases in Creuse showed a progressive increase over years, with a peak in 2008 and a subsequent decrease. This trend contrasted with the national cases that showed an opposite pattern. CONCLUSIONS Local environmental conditions were most likely responsible for a transient expansion of pathogenic Y. enterocolitica strains in Creuse.

Characterisation of atypical biotype 3, serotype O:3 Yersinia and development of a simple identification scheme.

Five clinical strains ofYersinia isolated in Japan and identified as atypical biotype 3 or biotype 3B, serotype O∶:3, phage type II (3*/O∶3/II)Yersinia enterocolitica were characterised since the biochemical reactions of these strains indicate they might also belong to the speciesYersinia bercovieri. Biochemical tests, characterisation of the β-lactamases and DNA-DNA hybridization studies provided strong evidence indicating that these strains should be classified asYersinia enterocolitica. A simple scheme combining a disc diffusion test and four biochemical tests was devised for identification of these atypical strains.